System and method for lithography process monitoring and control

ABSTRACT

In one aspect, the present invention is a technique of, and a system and sensor for measuring, inspecting, characterizing and/or evaluating optical lithographic equipment, methods, and/or materials used therewith, for example, photomasks. In one embodiment, the system, sensor and technique measures, collects and/or detects an aerial image produced or generated by the interaction between the photomask and lithographic equipment. An image sensor unit may measure, collect, sense and/or detect the aerial image in situ—that is, the aerial image at the wafer plane produced, in part, by a product-type photomask (i.e., a wafer having integrated circuits formed during the integrated circuit fabrication process) and/or by associated lithographic equipment used, or to be used, to manufacture of integrated circuits. In this way, the aerial image used, generated or produced to measure, inspect, characterize and/or evaluate the photomask is the same aerial image used, generated or produced during wafer exposure in integrated circuit manufacturing. In another embodiment, the system, sensor and technique characterizes and/or evaluates the performance of the optical lithographic equipment, for example, the optical sub-system of such equipment. In this regard, in one embodiment, an image sensor unit measures, collects, senses and/or detects the aerial image produced or generated by the interaction between lithographic equipment and a photomask having a known, predetermined or fixed pattern (i.e., test mask). In this way, the system, sensor and technique collects, senses and/or detects the aerial image produced or generated by the test mask—lithographic equipment in order to inspect, evaluate and/or characterize the performance of the lithographic equipment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to: (1) U.S. Provisional ApplicationSer. No. 60/386,408, entitled “Complete Optical Lithography Inspectionand Process Control”, filed Jun. 7, 2002; and (2) U.S. ProvisionalApplication Ser. No. 60/432,725, entitled “Method and Apparatus forAerial Imaging”, filed Dec. 12, 2002. The contents of these provisionalapplications are incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

This invention relates to lithographic systems and techniques that areused in, for example, integrated circuit manufacturing; and moreparticularly, in one aspect, to measure, inspect, characterize and/orevaluate optical lithographic equipment, methods, and/or sub-systemsrelated thereto (for example, the optical sub-systems and controlsystems of the equipment as well as photomasks used therewith).

In the fabrication of integrated circuit, lithography is employed to“print” circuit patterns on a wafer (e.g., silicon or GaAs semiconductorsubstrate). Currently, optical lithography is the predominant form oflithography used in volume integrated circuit manufacturing. Opticallithography typically employs visible or ultraviolet light to expose agiven pattern (generally defined by the photomask) on the resist that isdisposed on a wafer to be transferred into the substrate through resistdevelopment and subsequent process steps, for example, etching,deposition and implantation

In optical lithography, the photomask (or mask), is first written usingelectron-beam or laser-beam direct-write tools. The mask containscertain patterns and features that are used to create desired circuitpatterns on a wafer. The process of fabricating a complete integratedcircuit typically requires the use of many masks.

In the field of integrated circuit manufacturing, a common lithographictool used in projecting an image or pattern formed in a photomask onto awafer is known as a “stepper” or “scanner”. With reference to FIG. 1,lithographic equipment 10 (for example, a stepper) may include mirror12, light source 14 to generate light 16 at, for example, an exposurewavelength λ₀. The lithographic equipment 10 may also includeillumination optics 18, projection optics 20, and a chuck 22 upon whicha wafer 24 is temporally secured, typically by way of electrostatic orvacuum forces, in a wafer plane. The mask 26 is positioned and opticallyaligned to project an image of the circuit pattern to be duplicated ontowafer 24. The lithographic equipment 10 may employ a variety of wellknown stepping, scanning or imaging techniques to produce or replicatethe mask pattern on wafer 24.

In general, there are three stages at which the integrity of thelithography process is measured, characterized or inspected. First, themask is inspected to determine whether the pattern on the maskaccurately represents the desired mask design. Second, the optics of thestepper (for example, light source 14, illumination optics 18, andprojection optics 20) are measured or characterized to confirm that theyare within acceptable guidelines. Third, the pattern “printed” or formedon the wafer or die (discrete pieces of the wafer) is inspected andanalyzed to determine or measure the quality of the fabrication process.

The photomasks are typically inspected first by the photomask fabricatorbefore providing them to an integrated circuit manufacturer, and thenperiodically by the integrated circuit manufacturer, for example, duringinitial mask qualification and re-qualification. The fabricator andmanufacturer tend to use standalone equipment, for example, tools madeby KLA-Tencor (e.g., TeraStar series equipment) or Applied Materials(e.g., ARIS-1001 equipment). This standalone equipment, among otherthings, assesses the accuracy or integrity of the photomask as well asits ability to produce an accurate representation of the circuit designonto the wafer or die, when used in conjunction with appropriate stepperoptics and settings. While such inspection equipment may provide anaccurate representation of the photomask, it tends to be quite expensiveand hence its use tends to be minimized.

Moreover, such inspection equipment often employs optical imagingsystems (or sub-systems) that are fundamentally different from that usedby the stepper in “printing” the image on the wafer during massproduction. For example, such standalone tools may include opticalimaging systems that employ wavelengths that are different from opticalimaging systems used in the mass production steppers. The responseand/or characteristics of photomask may depend upon the wavelength ofthe light used to measure or detect the mask (via, for example, anaerial image). Indeed, a photomask may exhibit defects in the productionstepper environment that may not be detectable in the standaloneinspection tool because, for example, detection of certain contaminantsdepends on wavelength. That is, certain contaminants may present seriousissues at the wavelength used during production but may be undetectableat the wavelength used during inspection.

The optics of the stepper are typically characterized by themanufacturer after the stepper is manufactured using grating andwavefront interference methods. The manufacturer may also employscanning electron microscopy (SEM) techniques to measure the patternsprinted, formed or projected on test wafers. In this regard, themanufacturer typically uses photomasks having specifically designed testpatterns. In this way, a resist pattern developed on a test wafer may bemeasured using SEM techniques and compared to a known, predetermined,fixed or expected pattern.

Due primarily to complexity of the inspection techniques, the inspectionprocedure of the stepper tends to require or consume an extended periodof time, often days to complete, and thus represents an expensiveprocedure for the integrated circuit manufacturer to carry out.

The integrated circuit manufacturer, however, may inspect and evaluate astepper indirectly, using SEM inspection and analysis of the developedresist image. Here again, due to the extended test time, inspection ofthe stepper is not performed very often, and, as a result, there are fewsamples and/or data to form a reliable measure of the stepper.

Conventional techniques to evaluate the final printed circuit pattern onthe wafer or die tend to require examining the pattern formed on thewafer using SEM techniques. In this regard, the characterization orverification of the accuracy and quality of the circuit pattern permitsan indirect method of characterizing or verifying the mask and stepper(including optics), as well as the interactions between the mask andstepper. Because the final printed circuit pattern on the wafer or dieis formed after the resist development and may be after substratetreatment (for example, material etching or deposition), it may bedifficult to attribute, discriminate or isolate errors in the finalprinted circuit pattern to problems associated with the photomask, thestepper, or the resist deposition and/or the developing processes.Moreover, as with inspection of the optics of the stepper, inspectingthe final printed circuit pattern on the wafer or die using an SEM tendsto offer a limited number of samples upon which to detect, determine,and resolve any processing issues. This process may be labor intensiveand presents an extensive inspection and analysis time.

Thus, there is a need for a system and technique to overcome theshortcomings of one, some or all of the conventional systems andtechniques. In this regard, there is a need for an improved system andtechnique to inspect and characterize optical lithographic equipment,including the optical sub-systems, control systems and photomasks, thatare used in, for example, integrated circuit manufacturing.

In addition, there is a need for a system and technique of photomaskinspection and characterization of in-situ or in a massproduction/fabrication environment. In this regard, there is a need fora system and technique to measure, sense, inspect, detect, captureand/or evaluate the aerial image of a photomask in situ—that is, in themass production environment using the lithographic production equipmentof that environment. In this way, the errors may be isolated andattributed to a given aspect of the process or system. Indeed, thecauses of errors in a final printed circuit pattern may be isolated,characterized and/or measured (in, for example, the photomask, stepper,and/or resist developing process) so that appropriate correctivemeasures may be determined efficiently, rapidly and in a cost-effectivemanner. Thus, there is a need for a system and technique that permitserrors in the lithographic fabrication process to be attributed orisolated to certain methods or equipment (for example, the photomask oroptical sub-system) in order to facilitate appropriate and/or efficientcorrection of such errors in the final printed circuit pattern andthereby enhance or improve the quality, yield and cost of integratedcircuits.

Further, there is a need for an improved lithographic image evaluationtechnique and system that overcomes one, some or all of the conventionalsystems and techniques. In this regard, there is a need for a system andtechnique to more thoroughly, quickly and/or more often evaluate andcalibrate lithographic imaging systems, for example, steppers, in anefficient and cost-effective manner. In this way, the quality, yield andcost of integrated circuits may be improved.

SUMMARY OF THE INVENTION

There are many inventions described herein. In a first principal aspect,the present invention is an image sensor unit, for use with a highlyprecise moveable platform. The image sensor unit of this aspect of theinvention includes a substrate having a wafer-shaped profile or formfactor that may allow automated handling of image sensor unit in thesame manner as a product-type wafer. The image sensor unit furtherincludes a sensor array (for example, charge coupled, CMOS or photodiodedevices) disposed on the substrate.

The sensor array includes a plurality of sensor cells wherein eachsensor cell includes an active area to sense light of a predeterminedwavelength that is incident thereon. The sensor array also includes afilm, disposed over the active areas of sensor cells and comprised of amaterial that impedes passage of light of the predetermined wavelength.The film includes a plurality of apertures that are arranged such thatat least one aperture overlies an active area of a corresponding sensorcell to expose a portion of the active area and wherein light of thepredetermined wavelength is capable of being sensed by the portion ofthe active area that is exposed by the corresponding aperture.

In one embodiment of this aspect of the invention, the image sensor unitmay include a transparent medium, having a predetermined refractiveindex, disposed on the sensor array. In another embodiment, the imagesensor unit may include photon-conversion material disposed over and/orwithin the sensor array. The photo-conversion material may be disposedbetween the film and the plurality of sensors.

In another embodiment, the image sensor unit may include communicationscircuitry disposed on the substrate. The communications circuitry mayemploy wired, wireless and/or optical techniques. In one embodiment, thecommunications circuitry outputs data from the sensor array, using wiredand/or wireless techniques, during collection of image data by thesensor array.

In another embodiment, the image sensor unit may include at least onebattery, disposed on the wafer-shaped substrate or within a cavity inthe wafer-shaped substrate. The battery may be rechargeable and mayprovide electrical power to the sensor array and/or the communicationscircuitry.

In another embodiment, the image sensor unit may also include datastorage circuitry and data compression circuitry. In this embodiment,the data storage circuitry is coupled to the sensor array to receive andstore the data from the sensor array. The data compression circuitry iscoupled to the data storage circuitry to compress the data.

In another principal aspect, the present invention is an image sensorunit, for use with a highly precise moveable platform, which includes awafer-shaped substrate and a sensor array, integrated into thesubstrate. The sensor array includes a plurality of sensor cells (forexample, charge coupled devices, CMOS devices or photodiodes) whereineach sensor cell includes an active area to sense light of apredetermined wavelength that is incident thereon. The sensor array alsoincludes a film, disposed over the plurality of active areas of thesensor cells and comprised of a material that impedes passage of lightof the predetermined wavelength. The film includes a plurality ofapertures that are arranged such that an aperture of the plurality ofapertures overlies an active area of a corresponding sensor cell toexpose a portion of the active area. In this way, light of thepredetermined wavelength is capable of being sensed by the portion ofthe active area that is exposed by the corresponding aperture.

In one embodiment of this aspect of the present invention, the imagesensor unit may include communications circuitry disposed on thesubstrate. The communications circuitry may employ wired, wirelessand/or optical techniques. In one embodiment, the communicationscircuitry outputs data from the sensor array, using wireless techniques,during collection of image data by the sensor array.

In another embodiment, the image sensor unit may include at least onebattery, disposed on the wafer-shaped substrate or within a cavity inthe wafer-shaped substrate. The battery may be rechargeable.

In yet another embodiment, the image sensor unit may also include datastorage circuitry and data compression circuitry. In this embodiment,the data storage circuitry is coupled to the sensor array to receive andstore the data from the sensor array. The data compression circuitry iscoupled to the data storage circuitry to compress the data.

The image sensor unit may include photon-conversion material disposedover and/or within the sensor array. In another embodiment, thephoto-conversion material is disposed between the film and the pluralityof sensors.

In yet another principal aspect, the present invention is a system tocollect image data which is representative of an aerial image of a mask(for example, a product-type or test mask) that is projected on a waferplane. The system includes an optical system to produce the image of themask on the wafer plane, a moveable platform and an image sensor unit,disposed on the moveable platform, to collect image data which isrepresentative of the aerial image of the mask.

The image sensor unit includes a wafer-shaped substrate and a sensorarray. The sensor array is disposed on or in the wafer-shaped substrate,such that when position on the moveable platform, the sensor array isdisposed in the wafer plane.

The sensor array includes a plurality of sensor cells wherein eachsensor cell includes an active area to sense light of a predeterminedwavelength that is incident thereon. The sensor array further includes afilm, disposed over the active areas of the sensor cells. The film iscomprised of a material that impedes passage of light of thepredetermined wavelength and includes a plurality of apertures which arearranged such that an aperture of the plurality of apertures overlies acorresponding active area of a corresponding sensor cell to expose aportion of the active area. In this way, the light of the predeterminedwavelength is capable of being sensed by the portion of the active areathat is exposed by the corresponding aperture.

In one embodiment of this aspect of the present invention, the imagesensor unit may include communications circuitry disposed on thesubstrate. The communications circuitry may employ wired, wirelessand/or optical techniques. In one embodiment, the communicationscircuitry outputs data from the sensor array, using wired and/orwireless techniques, during collection of image data by the sensorarray.

In another embodiment, the image sensor unit may include a dataprocessing unit and/or at least-one battery (for example, arechargeable-type), disposed on, or within a cavity in, the wafer-shapedsubstrate, to provide electrical power to the sensor array and/or thecommunications circuitry. The data processing unit may be configured toreceive the image data which is representative of the aerial image.

In one embodiment, the moveable platform may move in first and seconddirections to a plurality of discrete locations wherein at each discretelocation, the sensor cells sample the light incident on the exposedportion of the active area. The data processing unit may use the data togenerate the aerial image.

The distance between the plurality of discrete locations in the firstdirection may be less than or equal to the width of the apertures.Further, the distance between the plurality of discrete locations in thesecond direction may be less than or equal to the width of theapertures. In one embodiment, the processing unit interleaves the imagedata to generate the aerial image.

In one embodiment, the image sensor unit collects data which isrepresentative of the aerial image in a raster-type manner. In anotherembodiment, the image sensor unit collects image data which isrepresentative of the aerial image in a vector-type manner.

In another aspect, the present invention is an image sensor unit thatmay be employed to collect image data which is representative of anaerial image of a mask (for example, a product-type mask) that isprojected on a wafer plane by a lithographic unit. The image sensor unitof this aspect of the invention includes a sensor array which isdisposed in the moveable platform of the lithographic unit and capableof being located in the wafer plane. The sensor array (for example, acharge coupled, CMOS or photodiode device) includes a plurality ofsensor cells wherein each sensor cell includes an active area to senselight of a predetermined wavelength that is incident thereon. The sensorarray also includes a film, disposed over the active areas of theplurality of sensor cells and comprised of a material that impedespassage of light of the predetermined wavelength. The film includes aplurality of apertures which are arranged such that an aperture of theplurality of apertures overlies a corresponding active area of acorresponding sensor cell to expose a portion of the active area so thatlight of the predetermined wavelength is capable of being sensed by theportion of the active area that is exposed by the correspondingaperture.

In one embodiment, the sensor array is capable of being moved between aplurality of discrete locations in first and second directions whiledisposed on the moveable platform. The sensor cells sample the lightincident on the exposed portion of the active area at each discretelocation. The distance between the plurality of discrete locations inthe first direction may be less than or equal to the width of theapertures. Further, the distance between the plurality of discretelocations in the second direction may be less than or equal to the widthof the apertures. In one embodiment, the processing unit interleaves theimage data to generate the aerial image.

BRIEF DESCRIPTION OF THE DRAWINGS

In the course of the detailed description to follow, reference will bemade to the attached drawings. These drawings show different aspects ofthe present invention and, where appropriate, reference numeralsillustrating like structures, components, materials and/or elements indifferent figures are labeled similarly. It is understood that variouscombinations of the structures, components, materials and/or elements,other than those specifically shown, are contemplated and are within thescope of the present invention.

FIG. 1 is a block diagram representation of a conventional opticalstepper used in the fabrication process of an integrated circuit;

FIG. 2 is a block diagram representation of a system according to atleast one embodiment of the present invention;

FIGS. 3A-C are block diagram representations of a wafer-shaped imagesensor unit, according to certain embodiments of the present invention;

FIG. 3D is block diagram representation of an image sensor unitintegrated on or in a chuck of lithographic equipment, according to oneembodiment of the present invention;

FIG. 4 is a block diagram representation of a sensor array according toone embodiment of the present invention;

FIG. 5 is a two-dimensional (top view) schematic representation of thesensor array, in conjunction with a selectively patterned, shaped and/oretched opaque film, according to one embodiment of the presentinvention;

FIGS. 6A and 6B are cross-sectional views of the sensor array, inconjunction with a selectively patterned, shaped and/or etched opaquefilm, according to certain embodiments of FIG. 5;

FIGS. 7A and 7B are cross-sectional views of a sensor array, inconjunction with a selectively patterned, shaped and/or etched opaquefilm as well as a transparent medium of a predetermined refractiveindex, according to several embodiments of the present invention;

FIGS. 8A, 8B, 9A-D, 10 and 11A-C are cross-sectional views of the sensorcells and/or sensor array according to other embodiments of the presentinvention;

FIGS. 12A-C and 13A-E are representations of the image collectiontechniques, in relation to the sensor array, according to certainaspects of the present invention;

FIGS. 14A-C are representations of image collection techniques, inrelation to the sensor array, according to certain aspects of thepresent invention;

FIGS. 15A and 15B are exemplary representations of an image collectiontechnique, in relation to a sensor array that is smaller than the aerialimage to be collected, according to certain aspects of the presentinvention;

FIG. 16 is a representation of an image collection technique, inrelation to the sensor array, according to another aspect of the presentinvention; and

FIG. 17 is a representation of the image collection technique, inrelation to the sensor array, according to another aspect of the presentinvention;

FIGS. 18A and 18B are block diagram representations of a sensor arrayhaving a plurality of sub-sensor arrays; and

FIGS. 19 and 20 are exemplary representations of image collectiontechniques, in relation to a sensor array that is smaller than theaerial image to be collected, according to certain aspects of thepresent invention.

DETAILED DESCRIPTION

There are many inventions described herein. In one aspect, the presentinvention is directed to a technique of, and system for measuring,inspecting, characterizing and/or evaluating optical lithographicequipment, methods, and/or materials used therewith, for example,photomasks. In this regard, the present invention is a system, sensorand technique to sample, measure, collect and/or detect an aerial imageproduced or generated by the interaction between the photomask andlithographic equipment. An image sensor unit may be employed to sample,measure, collect and/or detect the aerial image of a product-typephotomask (i.e., a photomask that is used in the production ofintegrated circuits on product wafers) in situ—that is, the aerial imageat the wafer plane produced by the interaction between the photomask andthe lithographic equipment that are used (or to be used) duringmanufacture of integrated circuits. In this way, the aerial image used,generated or produced to measure, inspect, characterize and/or evaluatethe photomask is the same aerial image used, generated or producedduring wafer exposure in integrated circuit manufacturing.

In another aspect, the present invention is a technique of, and systemand sensor for measuring, inspecting, characterizing, sensing and/orevaluating the performance of the optical lithographic equipment, forexample, the optical sub-system of such equipment. In this regard, inone embodiment, an image sensor unit measures, collects, senses, and/ordetects the aerial image produced or generated by the interactionbetween lithographic equipment and a photomask having a known,predetermined or fixed pattern (i.e., test mask). The sensor unitsenses, collects and/or detects the aerial image produced or generatedby the test mask—lithographic equipment in order to measure, inspect,and/or characterize the performance of the optical sub-system of thelithographic equipment.

In another aspect, the present invention is a technique of, and imagingsystem and sensor for generating or producing the same or substantiallythe same aerial image (or producing, sampling, collecting and/ordetecting information relating to), with the same or substantially thesame spatial resolution, as certain lithographic equipment (for examplea particular stepper system having a given set of parameters, featuresor attributes). Here, the imaging system emulates that lithographicequipment. As such, the imaging system includes a precision mechanicalmovement stage having the same or substantially the same mechanicalprecision and controllability as lithographic equipment. The imagingsystem may be employed as a standalone aerial image monitoring tool thatmay be used in the reviewing of the aerial image of a mask under thepredetermined optic sub-system.

This “standalone tool” may be designed and fabricated to have one ormore of the following parameters that is/are the same or substantiallythe same as one or more of the following features or parameters of thelithographic equipment: (1) wavelength of light; (2) characteristics oflight source (e.g., excimer laser); (3) illumination system includingpartial coherence; and (4) numerical aperture (NA). In this way, thedifferences in the aerial image collected, sampled, produced, and/ormeasured using the imaging system and the sensor, in relation to thelithographic equipment, may be minimized and/or reduced. Moreover, thestandalone tool of this aspect of the invention may be a “mini-stepper”(which has a much smaller field than a production stepper, but otherwisesubstantially the same imaging properties).

In certain embodiments of the invention, the image sensor unit may bedisposed on, or integrated in a wafer-shaped platform or substrate. Thesensor of this embodiment includes a profile (for example, height andshape, and flatness of the sensing cells of the sensor) that facilitatesimplementation in lithographic equipment much like a product-type waferand maintains a stage position along the optical axis similar to, orsubstantially similar to, that of a product wafer. In this regard, thewafer-shaped sensor may be secured to the chuck and reside in the waferplane in a manner similar to a product-type wafer. Moreover, thewafer-shaped platform may permit automated handling by a robotic loaderof the lithographic equipment. In addition, electrical power may besupplied to the image sensor unit by a battery (rechargeable orotherwise) and/or the lithographic equipment; and data/commandtransmission may be accomplished using wired, wireless and/or opticaltechniques.

In other embodiments, the image sensor unit may be disposed in, orintegral with a subsystem, for instance, the wafer chuck of thelithographic equipment. In this way, the image sensor unit need not beloaded into the lithographic equipment but may be positioned in thewafer plane during inspection, characterization and/or evaluation of aphotomask and/or the optical system of the lithographic equipment. Theelectrical power may be provided to the image sensor unit from thelithographic equipment. Moreover, the image sensor unit mayreceive/provide data and commands using wired, wireless, or opticalcommunications.

Thus, in one aspect, the present invention measures, inspects,characterizes and/or evaluates photomasks directly, and in the actualproduction environment in which the photomasks are used during themanufacture of integrated circuits (i.e., employing the same orsubstantially the same lithographic equipment used during integratedcircuit fabrication or production). In another aspect, the presentinvention measures, inspects, characterizes and/or evaluates the opticalsystem of lithographic equipment using a photomask having a known,predetermined or fixed pattern.

In another aspect, the present invention is an image sensor thatincludes an array of sensor cells wherein each sensor cell includes anenhanced, limited or restricted spatial resolution. In this regard, eachsensor cell has “effective” active or photon sensitive area that is lessthan or substantially less (i.e., greater than 50%) than the active orphoton sensitive area of the sensor cell. The image sensor unit of thisaspect of the present invention may be employed on or in a highlyprecise spatial positioning and/or moveable platform, for example thestage of a stepper. In this way, the image sensor may measure, detect,sense, collect and/or sample an aerial image projected or incidentthereon. The data measured, detected, sensed, collected and/or sampledby all sensor cells may be combined to construct the aerial image, or todeduce relevant information directly without constructing the aerialimage. The data may also be measured, detected, sensed, collected and/orsampled using vectoring (absolute coordinates) techniques or vectorscanning techniques.

With reference to FIG. 2, in one embodiment, aerial image sensing system100 of the present invention includes lithographic equipment 10 (forexample, a stepper), image sensor unit 102, and processor/controller104, for example, a computer and/or data or image processing unit. Thelithographic equipment 10 is similar to that described above withrespect to FIG. 1. That is, lithographic equipment 10 may include mirror12, light source 14 to generate light 16 at, for example, an exposurewavelength λ₀, illumination optics 18, projection optics 20, and a chuck22. The chuck 22 secures sensor unit 102 in a fixed location, using, forexample, electrostatic or vacuum forces.

The optics of lithographic equipment 10 (for example, light source 14,illumination optics 18, and projection optics 20) interacts with mask 26to project an aerial image onto image sensor unit 102. In oneembodiment, photomask 26 may be a product-type mask; that is, aphotomask used to form circuits during integrated circuit fabrication.As such, photomask 26, in one embodiment, contains the pattern to bereplicated or printed on a wafer that ultimately contains the circuitdesign (or a portion thereof) of the integrated circuit. In thisembodiment, image sensor unit 102 may be employed to evaluate theinteraction between photomask 26 and lithographic equipment 10 (whetherproduction or non-production equipment) as well as characterize theperformance of lithographic equipment 10.

In another embodiment, mask 26 may be a test mask that is used toinspect, characterize and/or evaluate the optical characteristics orresponse of lithographic equipment 10. In this regard, mask 26 mayinclude a fixed, predetermined and/or known pattern against which theaerial image collected, sensed, sampled, measured and/or detected byimage sensor unit 102 will be evaluated, measured, and/or compared. Inthis way, any errors or discrepancies in the aerial images may beisolated or attributed to the optical system of lithographic equipment10 and the performance of that system may be evaluated or characterized.

With continued reference to FIG. 2, image sensor unit 102 collects,measures, senses and/or detects the aerial image produced or generatedby lithographic equipment 10 in conjunction with photomask 26. The imagesensor unit 102 provides image data, which is representative of theaerial image, to processor/controller 104. The processor/controller 104,in response, evaluates and/or analyzes that data to inspect,characterize and/or evaluate photomask 26 and/or lithographic equipment10 (or sub-systems thereof, for example, the optical sub-system). Inthis regard, processor/controller implements data processing andanalysis algorithms to process the data from image sensor unit 102 toreconstruct a full or partial aerial image, or to extract desiredinformation directly without reconstructing a full or partial aerialimage. Such image processing may involve deconvolution or othertechniques familiar to those skilled in the art.

In addition, processor/controller 104 may use the data from sensor unit102, to perform and evaluate critical dimension measurements, and/orconduct defect inspection, for example, by comparing the measured aerialimage to pattern design database, or do die-to-die inspection if thereare multiple dice on the same mask. The processor/controller 104 mayalso implement algorithms that conduct or perform resist modeling and/orintegrated circuit yield analyses.

The processor/controller 104 may be employed as a control or operatorconsole and data/image processing device. The processor/controller 104may store algorithms and software that process the data representativeof the aerial image (received from image sensor unit 102), extractinformation, manage data storage, and/or interface with users/operators.The processor/controller 104 may be located near or next to lithographicequipment 10 or in another locale, which is remote from lithographicequipment 10.

The processor/controller 104 may also provide and/or apply appropriatecorrective measures to lithographic equipment 10 in order to enhance orimprove the performance or operation of lithographic equipment 10 and/orenhance or improve the interaction between mask 26 and lithographicequipment 10. In this way, the quality, yield and cost of integratedcircuits fabricated using lithographic equipment 10 and/or mask 26 maybe improved or enhanced.

It should be noted that processor/controller 104 may be a stand-aloneunit, as illustrated in FIG. 2, or partially or wholly integrated inlithographic equipment 10. In this regard, suitable circuitry inlithographic equipment 10 may perform, execute and/or accomplish thefunctions and/or operations of processor/controller 104 (for example,evaluation and/or analysis of the data representative of the aerialimage collected, measured, sensed and/or detected at the wafer plane).Thus, in one embodiment, the inspection, characterization and/orevaluation circuitry/electronics may be partially or wholly integratedinto lithographic equipment 10 and, as such, this “integrated system”may determine, assess, apply and/or implement appropriate correctivemeasures to enhance or improve its operation and thereby improve orenhance the quality, yield and cost of integrated circuits manufacturedtherein.

It should be further noted that processor/controller 104 may also bepartially or wholly integrated in, or on, image sensor unit 102. In thisregard, some or all of the functions and operations to be performed byprocessor/controller 104 may be performed, executed and/or accomplishedby suitable circuitry in, or on image sensor unit 102. As such, thecollection and analysis of data representative of the aerial image maybe less cumbersome in that a bus may be integrated and/or fabricated onor within image sensor unit 102 to facilitate communication of data andcommands to/from the circuitry used to measure, detect and/or sense theaerial image and the circuitry used to evaluate and/or analyze the datarepresentative of the aerial image.

It should be noted that, in at least one embodiment,processor/controller 104 may interact with multiple sensor units 102and/or multiple lithographic equipment 10.

With reference to FIG. 3A, in one embodiment, image sensor unit 102includes sensor array 106, controller 108, batteries 110, datacompression circuitry 112, transmitter circuitry 114, andtransmitter/receiver circuitry 116. The image sensor unit 102 may beformed in or on substrate 118. The substrate 118, and, in particular,image sensor 102, may include a size and shape that facilitates imagesensor 102 being accepted by, or installed or mounted on chuck 22 oflithographic equipment 10 in a manner that is similar to that of aproduct wafer. As such, image sensor unit 102, and in particular sensorarray 106, may reside in the wafer plane so the aerial image measured,collected, sensed or detected is the same (or substantially the same) asthe aerial image projected on a product wafer by the interaction of mask26 and lithographic equipment 10.

Moreover, the wafer-shaped size and shape of image sensor unit 102 maypermit normal and/or typical operation of lithographic equipment 10. Inthose instances where lithographic equipment 10 includes automatedloading of wafers, the wafer-shaped profile or form factor of imagesensor 102 may allow automated handling of image sensor unit 102 in thesame manner as a product-type wafer. Indeed, in a preferred embodiment,the wafer-shaped size and shape of image sensor 102 includes a physicalform factor that permits the wafer handling apparatus (whether automatedor partially or fully manual) of lithographic equipment 10 to manipulatethe image sensor 102 without significant modifications to the waferhandling apparatus. In this way, the “down-time” of lithographicequipment 10, due to inspection and/or characterization of theinteraction between mask 26 and lithographic equipment 10, may beminimized.

The sensor array 106 may be a plurality of photo or photon sensitivedetectors or sensor cells that measure, sense, detect and/or collectincident energy or radiation, for example, incident visible orultraviolet light (for example, deep ultraviolet light). With referenceto FIG. 4, in one embodiment, sensor array 106 includes a plurality ofsensor cells 200 a ₁-200 a ₈, 200 b ₁-200 b ₈, 200 c ₁-200 c ₈, 200 d ₁to 200 d ₈, 200 e ₁-200 e ₈, 200 f ₁-200 f ₈, 200 g ₁-200 g ₈, and 200 h₁-200 h ₈, arranged or configured in a two dimensional array. The sensorcells 200 a _(x)-200 h _(x) (x=1 to 8) of sensor array 106 may becomprised of light or radiation sensing semiconductor devices, forexample, charge coupled devices (CCDs), CMOS sensor cells and/or photodiodes.

With continued reference to FIG. 4, sensor cells 200 a _(x)-200 h _(x)(x=1 to 8) include active area 202 a _(x)-202 h _(x) (x=1 to 8),respectively. The active area 202 a _(x)-202 h _(x) is that portion orarea of sensor cells 200 a _(x)-200 h _(x) (x=1 to 8), respectively,which is sensitive to the energy or radiation incident thereon. Thedimensions of active areas 202 a _(x)-202 h _(x) (x=1 to 8) may impactthe spatial resolution of the aerial image.

In those instances where the dimensions of active areas 202 a _(x)-202 h_(x) (x=1 to 8) are too large to provide a desired or required spatialresolution, it may be necessary to limit, restrict and/or reduce thephoto-sensitive area of sensor cells 200 a _(x)-200 h _(x) (x=1 to 8).With reference to FIGS. 5 and 6, sensor array 106, in one embodiment,may include a patterned opaque film 204 that impedes, obstructs, absorbsand/or blocks passage of photons or light of a given wavelength (thatis, at the wavelength to be measured, sensed or detected by sensor cells200 a _(x)-200 h _(x), x=1 to 8).

The opaque film 204 includes apertures 206 a _(x)-206 h _(x) (x=1 to 8).The apertures 206 a _(x)-206 _(x) (x=1 to 8) are configured or arrangedto overlie a respective one of active area 202 a _(x)-202 h _(x) (x=1 to8). In this way, opaque film 204 overlies sensor cells 200 a _(x)-200 h_(x) (x=1 to 8) to partially cover active areas 202 a _(x)-202 h _(x)(x=1 to 8) and thereby limit the photo-sensitive area of active area 202a _(x)-202 h _(x) (x=1 to 8) to the portion(s) effectively exposed byapertures 206 a _(x)-206 h _(x) (x=1 to 8). The portion of active area202 a _(x)-202 h _(x) (x=1 to 8) that is covered by film 204 does notmeasure, sense, detect and/or collect incident energy or radiation or issubstantially unaffected by such energy or radiation. As such, thespatial resolution of the energy measured by sensor cells 200 a _(x)-200h _(x) (x=1 to 8) is enhanced or improved because the portion or area ofthe sensor cell that is effectively exposed to, and/or measures, senses,detects and/or collects energy or radiation is limited or restricted.

In certain embodiments, it may be advantageous to selectively patternopaque film 204 to include apertures 206 a _(x)-206 h _(x) (x=1 to 8)that are located or positioned in, or near, the center of active areas202 a _(x)-202 h _(x) (x=1 to 8). In this way, a significant number ofphotons that enter apertures 206 a _(x)-206 h _(x) (x=1 to 8) may becollected, measured, sensed and/or detected by the underlying activeareas 202 a _(x)-202 h _(x) (x=1 to 8), respectively, regardless ofscattering caused or induced by apertures 206 a _(x)-206 h _(x) (x=1 to8). In addition, locating or positioning apertures 206 a _(x)-206 h _(x)(x=1 to 8) at or near the center of active areas 202 a _(x)-202 h _(x)(x=1 to 8) may ease alignment constraints during fabrication of opaquefilm 204 and apertures 206 a _(x)-206 h _(x) (x=1 to 8).

The opaque film 204 may be any material that may be deposited, grownand/or formed on or in sensor cells 200, and patterned, shaped and/oretched such that active areas 202 receive, measure, collect photons froma smaller, limited and/or restricted area or region (substantially orproportionally equal to the area of apertures 206 relative to the entireactive area). The opaque film 204 may be a metal or other material (forexample, ploy-silicon or amorphous-silicon) that effectively blocks thelight/radiation at the wavelength of concern. For example, opaque film204 may be a film, such as tungsten, silicon, platinum, aluminum,chromium, copper, gold, silver, or an oxide (for example, Ta₂O₅,tantalum-pentoxide) of a sufficient thickness to alter, modify, impede,obstruct, absorbs and/or block photons or light (of at least a givenwavelength) from being measured, sensed and/or detected by that portionof active area 202. In one embodiment, opaque film 204 may be tungstenof a thickness in the range of 100 nm. Indeed, any material that(wholly, substantially or effectively) alter or modifies photons orlight (of at least a given wavelength) from being measured, sensedand/or detected by a certain portion of active areas 202, and/or anymaterial that impedes, obstructs, absorbs and/or blocks passage of thewavelength of the photons to be measured, sensed or detected by sensorcells 200, whether now known or later developed, is intended to bewithin the scope of the present invention.

The opaque film 204 should be of sufficient thickness to wholly,partially or effectively impede, obstruct, absorb and/or block passageof the wavelength of the photons to be measured, sensed or detected bysensor cells 200. In certain embodiments, the thicker film 204, the moreeffective film 204 may be in impeding, obstructing, absorbing and/orblocking passage of at least the wavelength of interest. However, incertain instances, a thicker film may present more difficulties informing apertures 206 in film 204.

Moreover, a thicker film 204 may also present a higher aspect ratio(i.e., the ratio between aperture wall height and aperture diameter). Ahigher aspect ratio may allow less light impinging upon sensor cells 200to pass through apertures 206 as well as cause an aperture “response”function that is more complex than a summation of the photon energyimpinging on the inlet of aperture 206. In this regard, a higher aspectratio may cause opaque film 204 to block oblique rays (due, for example,to high NA optics) more than the film blocks rays having a straightangle. Further, higher aspect ratio increases the aperture responsefunction's dependence on the process variation, e.g., for the sameamount of sidewall angle variation between apertures, the apertureresponse changes more when the aspect ratio is higher. As such, in oneembodiment, the thickness of opaque film 204 is selected to be a minimumbut also sufficient to block, obstruct, and/or absorb the radiation tobe measured, sensed or detected by sensor cells 200.

In that regard, where the total light collecting area under the opaquefilm is A₁, and the aperture area is A₂, and assuming the signal fromthe aperture to be at least N times larger than the total signal fromthe blocked area (N can be called as the signal-to-noise-ratio, i.e.SNR, of the blocking), in one embodiment the attenuation of the opaquefilm to the light may be characterized as:D=N*(A ₁ /A ₂)

As such, where N=1000, A1 is 5 μm×5 μm, and A2 is 100 nm diameter, theattenuation factor D will need to be 3.2 e⁶.

The attenuation may be computed or characterized using the followingsteps:

(1) Penetration depth of the light in the film is: d=λ/(2*π*k), where λis the wavelength of light, and k is the imaginary part of therefractive index, which depends on the wavelength and material, and canbe looked up in material handbooks (see, for example, “Handbook ofOptical Constants of Solids”, Editor Edward D. Palik, Volume 1, 2, 3).The k value is usually in the range of 1.5 to 4.0. The larger the k, thesmaller the penetration depth and the better blocking.

(2) With the known penetration depth, the attenuation after thickness ofT is then:D=e^(T/d)

-   -   Hence, for a chosen opaque material and any specific wavelength,        the thickness T may be computed to achieve the required or        desired attenuation factor D. To give an order of magnitude,        using, for example, tungsten or polysilicon as the material for        opaque film 204, for 193 nm wavelength, and using the area ratio        used in the above example, the film thickness may be around 100        nm.

In one embodiment, as illustrated in FIG. 6B, opaque film 204 includes astep configuration around the proximity of apertures 206. Where opaquefilm 204 is fabricated from a metal material, a first layer or lowerstep may be deposited or formed and, at the same time or shortlythereafter, a second layer or upper step may be deposited or formedbetween apertures 206. In this embodiment, the configuration of opaquefilm 204 may effectively change the area ratio (A₁/A₂) to the area ratiobetween the surface of the lower layer of film 204 and aperture 206. Inone embodiment, this ratio may be less than 5.

Notably, in the example above, this embodiment may reduce therequirement on the attenuation ratio (D) by a factor of about 500, whichcould translate to about 40% reduction in the required aperture aspectratio (which may be characterized as the ratio between the thickness ofthe lower step metal film and the aperture diameter).

The apertures 206 in opaque film 204 may be formed using a millingtechnique (for example, focused beam of ions), etching technique (forexample, anisotropic plasma etching) combined with e-beam direct writetechniques. Indeed, any technique to form, create and/or produceapertures 206 in opaque film 204, whether now known or later developed,is intended to be within the scope of the present invention.

The size and shape of apertures 206 determine, to some extent, thenumber of photons sensed by sensor cells 200 and the maximum spatialfrequency of the measured aerial image. In one embodiment, apertures 206are substantially circular and have a diameter of between approximately50 nm to approximately 200 nm, and preferably between about 75 nm toabout 150 nm. An appropriate size of the diameter of apertures 206 maybe determined using the wavelength of the photons of light 16 and thenumerical aperture of lithographic equipment 10 (typical characterizedas n (i.e., the refractive index of the medium above the sensor or waferin lithographic equipment 10)×sin θ).

It should be noted that, for those skilled in image processing, it iswell known that, assuming the response of the aperture is a simplesummation of all photo energy impinged on it, the aperture will verylikely “behave” like a low pass-filter to the aerial image intensitydistribution. Assuming a square aperture of size d by d, the first zeroin the spatial frequency pass band may be at 1/d. If the aperture is around aperture with diameter d, the first zero in the spatial frequencypass band may be at 1.22/d. To preserve a substantial amount of, or allspatial information, 1/d (for square aperture) or 1.22/d (for roundaperture) should be higher than the maximum spatial frequency existingin the intensity distribution of the aerial image.

The discussion below may be applicable to round and/or square apertures.Moreover, the first zero in the spatial frequency pass band when theaperture size is d, where d is either the side length of a squareaperture, or 1/d is the diameter of a round aperture.

It should be further noted that a response function, which may be anacceptable approximation, is a summation of all the energy impinging onthe inlet of the aperture 206. More sophisticated response functionswill likely require detailed calibration and/or implementation ofsuitable computer simulations tools. Once such computer simulation toolis “TEMPEST” available from UC Berkeley.

Regardless of illumination, partial coherence, and/or ReticleEnhancement Techniques (for example, Optical Proximity Correction (OPC),and Phase-Shift Masks (PSM)) on masks, the maximum spatial frequency inthe light intensity distribution on wafer plane may be characterized as2×NA/λ, where NA is the Numerical Aperture of the stepper projectionoptics, and λ is the wavelength used in the imaging. Therefore, in oneembodiment, the aperture size that preserves all or substantially allspatial frequency, may be characterized as:1/d>2×NA/λ− or −d<λ/(2×NA)

In one embodiment, where lithographic equipment 10 includes an NA of0.75 and employs a wavelength of 193 nm, the size of apertures 206 maybe smaller than 128 nm. In those instances where lithographic equipment10 includes an NA of 0.65 employing a wavelength of 248 nm, the size ofapertures 206 may be smaller than 190 nm.

In certain instances, the smaller the size of aperture 206, the higherspatial frequencies can be preserved; in contrast, the smaller the sizeof apertures 206, the less light or radiation passes to sensor cells200. An aperture size smaller than λ/3 may severely reduce the lightthat can pass through, and aperture size smaller than λ/6 mayeffectively block the light passage. Therefore, in one embodiment, theaperture size is equal to or greater than λ/2. As such, for 193 nmwavelength, the aperture size may be 90 nm or greater; and for 248 nmwavelength, the aperture size may be 120 nm or greater.

Thus, in at least one embodiment, where the dimension size of activeareas 202 of sensor cells 200 are in the order of a few μm×a few μm (forexample, 2 μm×5 μm), and where a spatial resolution of between about 75nm to about 150 nm may be desired, required or advantageous, patternedfilm 204 (for example, tungsten, aluminum, or silicon) may be employedto limit or restrict the exposed active areas of sensor cells 200 a_(x)-200 h _(x) (x=1 to 8) thereby enhancing the spatial resolution ofsensor cells 200 a _(x)-200 h _(x) (x=1 to 8). A spatial resolution ofbetween about 75 nm and about 150 nm may be sufficient to properly,accurately and/or adequately characterize, measure, collect, senseand/or detect the aerial image of mask 26 as projected at the waferplane.

It should be noted that in one embodiment the sidewalls of apertures 206may be shaped to provide, among other things, an enhanced response.After dry etching or ion milling, the sidewall shape may be close tovertical. By shaping the walls of apertures 206, the shape can bemodified to have tilted angles, which may enhance the amount ofradiation that passes through apertures 206 for the oblique rays. Suchshaping may be by isotropic etching or other suitable technique.

The dimensions of sensor array 106 may depend, to some extent, on sizeof the aerial image to be measured, the technique employed to capturethat image, the data collection time, and/or any the spatial constraintsof sensor array 106 due to constraints imposed by image sensor unit 102and/or lithographic equipment 10. In one embodiment, sensor array 106may be the same, substantially the same or about the same size as theaerial image to be measured. In this way, the data collection time isminimized relative to a sensor array of substantially smaller size whilethe footprint of the sensor array is not too large. For example, wherethe aerial image at the wafer plane is about 26 mm×32 mm, sensor array106 may be about 27 mm×33 mm.

With reference to FIGS. 7A and 7B, in at least one embodiment, thesurface of sensor array 106 (or sensor cells 200) may be coated with atransparent medium 205 having predetermined refractive index “n”. In oneembodiment, the refractive index is equal to or substantially equal tothat of photoresist. In this way, a coating may: (1) reduce thewavelength to λ/n within apertures 206, and hence potentially increasethe light energy pass ratio by the aperture; (2) enhance the refractionto oblique rays to make the direction of oblique rays more “straightdown” toward apertures 206, and hence improve the passing ratio ofoblique rays; (3) emulate the refraction effect of resist on aerialimage, and thereby cause the sensed aerial image to be a closerapproximation of the aerial image “inside” resist; and/or (4) increasethe effective ratio between the aperture size and the wavelength (due tothe reduced wavelength inside the aperture), which may reduce theaperture response function's variation due to aperture process variation(for example, the variation in size between the apertures). In thisembodiment, transparent medium 205 may be deposited or grown afterformation of opaque film 204.

It should be noted that transparent medium 205 may be grown or depositedin apertures 206 rather than over all or substantially all of thesurface of sensor cells 200 or sensor array 106. In this embodiment,transparent medium 205 may be deposited or grown before or afterformation of opaque film 204.

It may be desirable, or in certain circumstances, advantageous, toenhance the photo-reception or photon efficiency of sensor cells 200.With reference to FIG. 8A, in one embodiment, a photo or photondetection enhancement material 208 a _(x)-208 h _(x) (x=1 to 8) (forexample, a photo or photon sensitive semiconductor material) may bedeposited, grown and/or formed within aperture 206 a _(m)-206 h _(x)(x=1 to 8), respectively, to enhance the ability or capacity of sensorarray 106 to measure, sample, sense and/or detect incident photons orenergy at a given wavelength (for example, λ₀). Thus, in thisembodiment, detection enhancement material 208 a _(x)-208 h _(x)enhances the ability or capacity of active areas 202 a _(x)-202 h _(x)(x=1 to 8) to measure, sample, sense and/or detect incident radiationand thereby improve the ability or capacity of sensor array 106 tocharacterize, measure, collect, sense and/or detect the aerial image ofmask 26 as projected at the wafer plane.

With continued reference to FIG. 8A, the detection enhancement material208 a _(x)-208 h _(x) (x=1 to 8) may be deposited, grown and/or formedbefore and/or after formation or patterning of apertures 206 a _(x)-206h _(x) (x=1 to 8). The detection enhancement material 208 a _(x)-208 h_(x) (x=1 to 8) may also be deposited, grown and/or formed before and/orafter deposition, growth or formation of opaque film 204. One examplefor the detection enhancement material 208 may be the semiconductormaterial used in the photo-sensitive area 202, so that photons can beconverted to electrons before they travel through the aperture.

With reference to FIG. 8B, in another embodiment, sensor array 106 mayinclude sensor cells 200 a _(x)-200 h _(x) (x=1 to 8) that areinsensitive (or relatively insensitive) to the wavelength of the energyemployed by the photolithographic equipment 10 to expose the waferduring integrated circuit fabrication (for example, photons or light atwavelength λ₀). The sensor array 106 may also include photon-conversionmaterial 210 a _(x)-210 h _(x) (x=1 to 8), for example, a “lumigen” or“lumogen” material, selectively disposed on active areas 202 a _(x)-202h _(x) (x=1 to 8) of sensor cells 200 a _(x)-200 h _(x) (x=1 to 8),respectively, to convert the energy into a form that is measurable bysensor cells 200 a _(x)-200 h _(x) (x=1 to 8). In this way, the activeareas 202 are effectively limited or reduced proportionally with thefootprint of photon-conversion material 210. Accordingly, thephoton-conversion material 210 enhances the spatial resolution of eachsensor cell 200.

For example, where sensor array 106 is employed in lithographicequipment 10 that utilizes ultraviolet light, for example, to projectthe aerial image at the wafer plane, sensor array 106 may include sensorcells 200 a _(x)-200 h _(x) (x=1 to 8) that are insensitive toultraviolet light, but measure, sample, sense, detect or collect photonsin the visible light spectrum. The photon-conversion material 210 a_(x)-210 h _(x) (x=1 to 8) may be selectively patterned and disposed onactive areas 202 a _(x)-202 h _(x) (x=1 to 8) of sensor cells 200 a_(x)-200 h _(x) (x=1 to 8), respectively, to convert ultraviolet lightincident on photon-conversion material 210 a _(x)-210 h _(x) (x=1 to 8)to visible light energy (or other wavelength of light that is sensitiveto the sensor cells). Thus, the exposed active areas of sensor cells 200a _(x)-200 h _(x) (x=1 to 8) are effectively limited or restricted whichthereby enhances the spatial resolution of sensor cells 200 a _(x)-200 h_(x) (x=1 to 8).

The photon-conversion material 210 a _(x)-210 h _(x) (x=1 to 8) may beselectively patterned and disposed on or over active areas 202 a_(x)-202 h _(x) (x=1 to 8) to provide an “effective” active area ofabout 75 nm to about 150 nm. As mentioned above, a spatial resolution ofabout 75 nm to about 150 nm may be sufficient to properly, accuratelyand/or adequately characterize or detect the aerial image of mask 26 asprojected at the wafer plane.

With reference to FIG. 9A, in another embodiment, opaque film 204 (ofFIGS. 6A and 6B) is used, in conjunction with photon-conversion material210 (of FIG. 8B) to enhance the resolution of sensor sells 200 a_(x)-200 h _(x) (x=1 to 8) of sensor array 106. In this regard, opaquefilm 204 and photon-conversion material 210 are disposed on or over atleast active areas 202 a _(x)-202 h _(x) (x=1 to 8) of sensor cells 200a _(x)-200 h _(x) (x=1 to 8), respectively. The active areas 202 a_(x)-202 h _(x) (x=1 to 8) of sensor cells 200 a _(x)-200 h _(x) (x=1 to8), respectively, measure, sample, sense, detect and/or are responsiveto visible light. The photon-conversion material 210 converts energy ofa given wavelength to visible light, as described above with respect toFIG. 8A. The opaque film 204 overlies or covers selected portions of thephoton-conversion material 210 and active areas 202 a _(x)-202 h _(x)(x=1 to 8) and forms apertures 206 a _(x)-206 h _(x) (x=1to 8) in thesame manner as described above with respect to FIGS. 5, 6A and 6B. Assuch, opaque film 204 limits or restricts the photons (of a givenwavelength) incident on the exposed photon-conversion material 210which, in turn, limits or restricts conversion of the incident photonsto visible light to those portions of active areas 202 a _(x)-202 h _(x)(x=1 to 8) that are incident or contiguous to the photon-conversionmaterial 210 exposed via apertures 206 a _(x)-206 h _(x) (x=1 to 8).

The embodiment of FIG. 9A may provide the advantage that the photons arestill at short ultraviolet wavelength when they pass through apertures206 of opaque film 204. As such, the scattering effect of the photonscaused by the apertures of opaque film 204 may be less severe which mayfacilitate more photons to pass or travel through the apertures 206, beconverted by photon-conversion material 210, and sampled, sensed,detected and/or measured by those portions of active areas 202 that arecontiguous with photon-conversion material 210 that is exposed byapertures 206 a _(x)-206 h.

With reference to FIG. 9B, in another embodiment, similar to theembodiments illustrated in FIGS. 7A and 7B, the opaque film 204 andphoton-conversion material 210 of FIG. 9A is coated with transparentmedium 205 having a refractive index “n”. In one embodiment, therefractive index of transparent medium 205 is equal to or substantiallyequal to that of photoresist. As mentioned above, such a coating may:(1) reduce the wavelength to λ/n within apertures 206; (2) enhance therefraction to oblique rays to make the direction of oblique rays more“straight down” toward apertures 206; (3) emulate the refraction effectof resist on aerial image; and (4) reduce the aperture responsevariation between apertures. The transparent medium 205 may be depositedor grown after formation of opaque film 204.

With reference to FIGS. 9C and 9D, photon-conversion material 210 mayalso be disposed in apertures 206 a _(x)-206 h _(x) (x=1 to 8) of film204. For example, photon-conversion material 210 may be deposited, grownand/or formed over sensor cells 200. Thereafter, film 204 may bedeposited, grown and/or formed over or in photo-conversion material 210and apertures 206 a _(x)-206 h _(x) (x=1 to 8) (see, for example, FIG.9C). Alternatively, photon-conversion material 210 may be deposited,grown and/or formed within apertures 206 a _(x)-206 h _(x) (x=1 to 8) ofopaque film 204 (see, for example, FIG. 9D). As described above, thephoton-conversion material 210 coverts photons of a given wavelength toanother wavelength which may be sensed, detected, measured or sampled byselected portions of active areas 202 a _(x)-202 h _(x) (x=1 to 8)defined, for example, by apertures 206 a _(x)-206 hx (x=1 to 8),respectively.

It should be noted that, in another embodiment, photon-conversionmaterial 210 may overlie or be disposed on opaque film 204. In thisregard, photon-conversion material 210 is deposited, grown and/or formedover opaque film 204. In operation, the photon-conversion material 210coverts photons of a given wavelength to energy of another wavelength(for example, visible light) which is then provided to selected portionsof active areas 202 a _(x)-202 h _(x) (x=1 to 8) defined by apertures206 a _(x)-206 h _(x) (x=1 to 8), respectively. In this way, the spatialresolution of sensor cells 200 is enhanced, limited and/or reduced

Moreover, with reference to FIG. 10, in another embodiment, a photo orphoton detection enhancement material 208 a _(x)-208 h _(x) (x=1 to 8)(for example, a photo or photon sensitive semiconductor material) may bedeposited, grown and/or formed within aperture 206 a _(x)-206 h _(x)(x=1 to 8), respectively, to enhance the efficiency of the active areas202 a _(x)-202 h _(x) (x=1 to 8) to receive and detect the visiblelight.

In another embodiment, sensor cells 200 having “effective” portions ofactive areas 202 of a suitable size may be fabricated by modifying theelectro-gate structure of the CCD cells, CMOS sensor cells, photodiodes, or other light sensing device. In this regard, in one aspect ofthis embodiment, an aperture in sensor cell 200 may be formed byselectively removing or eliminating certain material overlying theactive area of sensor cell 200. For example, with reference to FIG. 11A, an aperture in sensor cells 200 may be created by removing a portionof the layer(s) that obstructs, absorbs and/or impedes, for example,ultraviolet light. In this way, when implemented in an ultraviolet lightbased lithographic equipment, sensor cells 200 measure, collect, senseand/or detect photons having a wavelength in the ultraviolet region viathe aperture overlaying the active areas of sensor cells 200. Thistechnique and structure may be implemented in lithographic equipment orsystems employing other wavelengths or lithographic techniques. Thus,the technique and structure of this embodiment provides enhancedresolution of sensor cells 200 by selectively creating and/or forming anaperture in a certain portion of the layer(s) that obstructs, absorbs orimpedes photons of a wavelength to be measured by sensor cells 200.

It should be noted that the apertures in the electro-gate structure maybe created after fabrication of the sensor cells (for example, by ionmilling or e-beam lithography), or during its fabrication by modifyingthe mask used to create the electro-gate of the sensor cells. It shouldbe further noted that in this embodiment, the layer(s) in which theaperture is formed may be considered to be the same as opaque film 204discussed above.

In yet another embodiment, sensor cells 200 having “effective” portionsof active areas 202 of a suitable size may be fabricated byincorporating opaque film 204 (including apertures 206) within themultiple layers of CCD cells, CMOS sensor cells, photo diodes, or otherlight sensing device. In this regard, opaque film 204 is integrated intosensor cells 200 and disposed between a protective outer surface ofsensor cells 200 and active areas 202 of sensor cells 200. For example,with reference to FIG. 11B, opaque film 204 is disposed between activearea 202 and a protective layer of silicon dioxide (SiO₂) or siliconnitride (Si₃N₄). In this embodiment, opaque film 204 may be any materialthat may be deposited, grown and/or formed in sensor cells 200, andpatterned, milled, shaped and/or etched such that active areas 202receive, measure, collect photons from a smaller, limited and/orrestricted area or region (substantially or proportionally equal to thearea of apertures 206 relative to the entire active area 202). Thus, thetechnique and structure of this embodiment provides enhanced resolutionof sensor cells 200 by integrating an additional layer, i.e., opaquefilm 204 (having apertures 206), in sensor cell 200.

It should be further noted that there are many techniques and materials(and, as a result, structures created thereby) for enhancing the spatialresolution of sensor cells 200. Moreover, there are many techniques andpermutations of depositing, growing, milling and/or forming the variouslayers of sensor 200, opaque film 204, apertures 206, detectionenhancement material 208, and/or photon-conversion material 210. Forexample, with reference to FIG. 11C, detection enhancement material 208and/or photon-conversion material 210 may be disposed in or nearapertures 206 (via, for example, CVD, PECVD or implantation techniques)of the sensor cells illustrated in FIGS. 11A or 11B. Thus, alltechniques and materials, and permutations thereof, that enhance thespatial resolution of active areas 202 of sensor cells 200, whether nowknown or later developed, are intended to be within the scope of thepresent invention.

Moreover, in one embodiment, the sensor cells 200 of FIGS. 11A-C mayalso include transparent material 205 (having the predeterminedrefractive index “n”) disposed over apertures 206 and active areas 202of sensor cell 200. In another embodiment, the film 204 includes a stepconfiguration around the proximity of apertures 206 as illustrated inFIGS. 6B and 7B. The discussions of sensor array 200 of FIGS. 6A, 6B, 7Aand 7B are fully applicable to this aspect of the present invention.However, for the sake of brevity, those discussions will not berepeated.

With reference to FIGS. 3A, 3B and 3C, as mentioned above, image sensorunit 102 may also include controller 108, a source of electrical power,for example, batteries 110, data compression circuitry 112, transmittercircuitry 114, transmitter/receiver circuitry 116, memory 120 andconnector 122. The controller 108, data compression circuitry 112,transmitter circuitry 114, transmitter/receiver circuitry 116, and/ormemory 120 may be incorporated on image sensor unit 102 as discretecomponents or may be integrated in substrate 118 (via VLSI or LSIintegration techniques), or a combination thereof (for example, sensorarray 106 is integrated in substrate 118 and transmitter circuitry 114are discrete components). In those circumstances where the electronicsof image sensor unit 102 is comprised of discrete components it may beadvantageous to employ surface mount technologies, unpackaged die and/orcavities, holes or cut-outs in substrate 118 in order to furtherminimize the profile of sensor unit 102.

Further, in those circumstances where the electronics of image sensorunit 102 is comprised of discrete components, sensor unit 102 may be acircuit board-like structure which has the same or substantially thesame two-dimensional shape as a wafer. In these embodiments, thehybrid-type sensor wafer may be thicker than an actual product wafer,where surface topography of substrate 118 and sensor unit 102 may not beflat or uniform. In one preferred embodiment, however the thicknessrange of sensor 102 is within the acceptable parameters to be handled bylithographic equipment 10.

The substrate 118 may be a blank silicon wafer, or be made of some othermaterial (e.g., aluminum carbide) suitable to be placed on a stepperstage. The discrete components may be disposed onto the substrate, andinterconnected through patterned metal wires on or in the substrate orvia bonding wires.

For example, where sensor 102 is used in conjunction with lithographicequipment 10 (for example, a stepper), the: (1) total weight of sensorunit 102 preferably should be within a range from an actual wafer, hencebe able to be handled by the stage control system and wafer handlingsystems; and (2) the thickness of sensor unit 102 preferably should bewithin a range from actual wafers so that the stage may handle to keepthe appropriate focus on the surface of sensor array 106. Of particularinterest is a configuration that maintains sensor array 106, andpotentially a focus area around it, at the same thickness as a typicalwafer, so that the auto-focus system of lithographic equipment 10 (ifany) may achieve focus on the surface of sensor array 106 withoutadjusting the Z-height of the wafer stage. It should be noted that areasoutside sensor array 106 may not need to have the same thickness of atypical wafer. Preferably, however, there is enough “clearance” relativeto the working distance of stepper optics and other wafer handlingsystems to permit automatic handling and/or placement on chuck 22 withno or minimal modification to lithographic equipment 10.

In those instances where sensor array 106 is a discrete device (or ismanufactured in or on substrate 118), the “flatness” of the surface ofsensor array 106 may be an important consideration, because for thesensor array to measure, sense, sample and detect useful information,all cells in the array need to lie within the depth of focus oflithographic equipment 10. For example, where lithographic equipment 10is a stepper having a numerical aperture NA and using a radiation sourceof wavelength λ, the depth of focus may be characterized as λ/(NA)². Assuch, for 193 nm stepper with NA=0.75, the depth of focus is 340 nm and,it may be preferable to maintain a surface flatness of sensor array 106smaller than the depth of focus, for example, within 100 nm.

It should be noted that in those situations where lithographic equipment10 employs UV light, it is preferable to employ a sensor array 106 thatis UV-stable (i.e., does not emit any significant contaminationdetrimental to lithographic equipment 10 (or portions thereof underillumination. Moreover, it may be advantageous to passivate sensor unit102 and/or sensor array 106, for example, with a coating of an inertmaterial, to enhance the structural and/or performance stability ofsensor unit 102 and/or sensor array 106. The sensor array 106 and/orsensor unit 102 may also be coated with anti-reflection materials toreduce reflecting light back into lithographic equipment 10 (forexample, the optical sub-system of lithographic equipment 10).

When using anti-reflection (AR) costing on the sensor array 106, thecoating may cover the entire sensor array 106, or may only cover thearea outside the apertures 206. The AR coating may be applied before orafter the apertures 206 are processed. When the AR is coated before theapertures are processed, the aperture processing may be drilling oretching the apertures through both the AR coating and the blocking layer204. To reduce the total aperture aspect ratio for the benefitsdescribed before, it is maybe advantageous to recess the AR coating fromthe aperture, so that the AR layer's thickness does not contribute tothe total aperture sidewall height. When fabricating the AR recess, itis similar to create the second layer of 204 as described above inconjunction with FIG. 6B and 7B. The recessed AR may be the secondlayer, or coincide with the second layer of 204, or be the third layer.

With continued reference to FIGS. 3A, 3B and 3C, in certain embodiments,controller 108 coordinates the operations and/or functions of thevarious electronics on or in image sensor unit 102. In this regard,controller 108 may coordinate the sampling of data by sensor array 106with the exposure and movement operations by lithographic equipment 10.The controller 108 may also coordinate the operation and/or timing ofthe data communication, data collection and storage, clocking,synchronization, and testing.

In particular, controller 108 may be employed to: (1) interpret andexecute the received commands, for example, from the input wired orwireless channel, (2) generate and manage clock signals for otherelectronics on sensor unit 102, (3) synchronize job start and operationsof sensor array 106, compression circuitry 112, and/or wired or wirelesstransmission (for example, Tx 114 and/or Tx/Rx 116); (4) monitor theoperating conditions of sensor array 106 and/or sensor unit 102 (forexample, temperature, power, and local current); (5) perform, implementand/or coordinate self-testing of the electronics on sensor unit 102(for example, sensor cells 200 of sensor array 106); (6) store andprovide calibration and/or implementation data of the electronics onsensor unit 102 (for example, sensor array 106 and/or compressioncircuitry 112); (7) store and provide operations information to theelectronics on sensor unit 102, including commands and operatingconditions; and (8) perform and schedule testing of sensor unit 102(based, for example, on historical information relating to testing andtest results). Indeed, such testing may include statistical processcontrol functions for sensor unit 102 and provide relevant warning orpreventative maintenance requests to processor/controller 104. Further,based on monitored information, sensor unit 102 may provide warningmessages or emergency shutdown safety functions.

The controller 108 may also have resident memory to store firmware,calibration data and/or sensor history. The controller, like the otherelectronics of sensor unit 102, may be implemented via FPGA, DSP,microprocessor or microcontroller, and/or an ASIC.

In certain embodiments, image sensor unit 102 may include a source ofelectrical power, for example, batteries 110 (for example, theembodiments of FIGS. 3A and 3B). In this regard, batteries 110 may be aprimary source of electrical power and thereby may provide all orsubstantially all of the power requirements of image sensor unit 102.The batteries 110 may be rechargeable (after one or several aerial imagecapture routines). For example, batteries 110 may include lithium-ionbased batteries and/or polymer based batteries. Where the invention isemployed in a clean room environment, for example, batteries 110 shouldbe stable and durable to prevent leakage.

The batteries 110 may be customized to accommodate the shape and profileconstraints of the wafer-shaped embodiments of sensor unit 102. Further,batteries 110 may be disposed in cavities, holes or cut-outs insubstrate 118 in order to minimize the profile of image sensor unit 102.Thus, image sensor unit 102 of these embodiments may be implemented inlithographic equipment 10 as a self-contained and/or self-sufficientsensing device without the need of electrical connection to lithographicequipment 10 or elsewhere.

In certain embodiments, the source of power may be provided to imagesensor unit 102 using connector 122 (see, for example, FIGS. 3B and 3C).In this way, some or all of the electronics may be powered by anexternal power source, which may facilitate use of higher powerconsumption components that may offer features not offered by lowerpower consumption components (for example, speed).

It should be noted that in those instances where image sensor unit 102is incorporated or integrated into chuck 22 of lithographic equipment10, power may be provided by lithographic equipment 10. In thisembodiment, as discussed in detail below, there may be no need to employbatteries 110, unless, for example, as an auxiliary or back-up powersource, in the event of a power failure to sensor unit 102.

With reference to FIGS. 3A, 3B and 3C, image sensor unit 102 may alsoinclude data compression circuitry 112 to compress the image data (forexample, 8 bits per pixel to represent a pixel's gray scale value)collected by sensor array 106 before transmission or communication toprocessor/controller 104. The data compression circuitry 112 may reducethe bandwidth requirements of the data communications. In thoseinstances where wireless transmission is employed to provide data toprocessor/controller 104, compression of the data (via circuitry 112)may significantly reduce the bandwidth requirements of transmittercircuitry 1 14 and transmitter/receiver circuitry 116 and, as such,provide the data representative of the aerial image toprocessor/controller 104 in a more efficient, less time consumingmanner. Compression of the data may also reduce the power consumption bysuch wireless transmission circuitry.

The data compression circuitry 112 may be in or on FPGA,microprocessors, DSP and/or ASIC(s). As mentioned above, in thosecircumstances where data compression circuitry 112 is a discretecomponent, it may be advantageous to employ surface mount technologies,unpackaged die and/or cavities, holes or cutouts in substrate 118 inorder to minimize the profile of sensor unit 102 (if necessary).

It is preferred to use lossless data compression techniques. In thisway, no information is lost in compression.

For an optical image of integrated circuit pattern, a 2:1 losslesscompression ratio may be suitable. Many compression algorithms aresuitable and are well known to those skilled in the art.

In one embodiment, to improve the compression ratio, the data may bearranged to improve the correlation between image data. In this regard,the image usually gives good correlation between neighboring pixels. Inthose instances where the data is provided to compression circuitry 112in its sequence of availability, for example, sub-frame by sub-frame. Asub-frame refers to the array of output of an array of sensor cells,when the sensor array is positioned at a fixed location relative to theaerial image. The sub-frame embodiments will be discussed in more detailbelow, for example, in conjunction with FIGS. 12A-C, 13A-E, and 14A-C),the inter-pixel correction may be minimum. As such, it may be desirableto setup a buffer (using, for example, memory 120) to store or maintainseveral (for example, 2, 4, or 8) sub-frames before providing the datato the compression engine of compression circuitry 112. The datasequence may be re-arranged in the buffer so that the values ofneighboring pixels (i.e., from neighboring sub-frames) are juxtaposed orstored in another predetermined arrangement that improves thecompression ratio.

In another embodiment, image processing is performed on the data priorto providing the data to the compression engine of compression circuitry112. For example, data which is representative of the aerial imagemeasured, sensed, detected and/or sampled by sensor cells 200 may beprocessed to reduce, minimize or eliminate the noise content within thedata. This may be accomplished using data from neighboring pixels.Thereafter, the pre-processed data may be provided to the compressionengine of compression circuitry 112 and the compressed data may betransmitted or communicated to processor/controller 104. By performingsome or all of the noise processing functions to image processingcircuitry on image sensor unit 102, the compression ratio may improve.

In those instances where the functions and/or operations ofprocessor/controller 104 are integrated on image sensor unit 102 or inlithographic equipment 10, there may be no advantage to compress thedata which is representative of the aerial image before transmission. Inthis regard, data may be provided to the transmission circuitry via aninternal bus in or on image sensor unit 102, or via connector 122directly to lithographic equipment 10 or to processor/controller 104. Inthis circumstance, it may be advantageous to employ a high-speed and/orwide data bus as a mechanism for data transmission from image sensorunit 102 to the appropriate circuitry of processor/controller 104.

With continued reference to FIGS. 3A, 3B and 3C, image sensor unit 102may employ wired, wireless and/or optical data transmission. In thoseinstances where wireless transmission is implemented as a technique toprovide some or all data and commands to/from image sensor unit 102(see, for example, FIGS. 3A and 3B), image sensor unit 102 may includetransmitter circuitry 1 14 and/or transmitter/receiver circuitry 116. Inthis way, image sensor unit 102 may be implemented in lithographicequipment 10 in the same manner as a product wafer. Moreover, where alldata and commands are provided via wireless techniques (see, forexample, FIG. 3A), image sensor unit 102 may be implemented inlithographic equipment 10 as a self-contained and/or self-sufficientunit without the need of electrical connection of any kind to/fromlithographic equipment 10.

In those embodiments where image sensor unit 102 employs wired and/oroptical data transmission, connector 122 may be disposed on substrate118 to provide a mechanism for external communication. The connector 122may be an electrical connector that includes signal, power and groundpins or contacts, where signals are transmitted using proprietary ornon-proprietary protocols. The connector 122 may also be an opticalconnector (for example, an optical transmitter/receiver) thatcommunicates signals using well-known protocols.

It should be noted that there are many wireless technologies that may beimplemented. For example, Radio Frequency (RF) based wirelesscommunication technologies may be more suitable than other free-spacetechniques because such techniques provide high data transfer rates butdo not require the presence of a line of sight. Other suitable wirelesstechnologies include, for example, infrared and free-space opticalcommunications. Indeed, all such wireless communication techniques,whether now known or later developed, are intended to be within thescope of the present invention.

In one embodiment, wireless local area network technologies, forexample, 802.11a/b/g, may be employed for the RF based wirelesstransmission. Indeed, in one embodiment, multiple channels of 802.11a/g(each channel supports 54 Mbps raw data rate) may be implemented tooutput data (for example, sensor data), and one channel of 802.11b (eachchannel supports 11 Mbps data rate) may be implemented to input data(for example, commands and/or configuration data). Moreover,implementing a configuration where there is short distance betweenantennas, the power consumption of these multiple channels may besignificantly reduced without adversely affecting the communicationquality.

Further, when using 802.1 1 technologies, or other general-purposecommunication techniques, the communication protocols may be slightlymodified to reduce the amount of overhead data, and hence increase theeffective payload bit rate of the communication channels. For example,the “top-layer” in 802.11, namely TCP (Transmission Control Protocol)may be eliminated, which would eliminate the header data associated withit. In this way, the amount of overhead data is reduced.

In those instances where RF wireless is implemented, an antenna may beplaced on or close/near to lithographic equipment 10 (for example, on orclose/near to the door of the stepper) to communicate with an antennadisposed on image sensor unit 102. The distance between the two antennasmay be very short, in the order of a few feet, which is the distancebetween the wafer stage and the stepper door. As such, the wirelesstransmission data rate may be high, in the range of hundreds of megabits per second.

After the data is received at the antenna outside lithographic equipment10, the data may be converted to other digital data formats, andprovided to processor/controller 104 using wired, wireless and/oroptical transmission (for example, wired Giga-bit Ethernettransmission). Implementing a wired or optical approach may minimize the“contamination” of the RF bands outside lithographic equipment 10. Inthis way, processor/controller 104 may be located some distance from thelithographic equipment 10, and even outside the clean room in thoseinstances where the lithographic equipment 10 is employed for integratedcircuit manufacture, for example.

In many embodiments, the output bandwidth requirement (i.e.,transmission of image data from sensor unit 102) is likely to be largerthan the input bandwidth (i.e., receipt of commands from, for example,processor/controller 104). In one embodiment, the output bandwidthsupports a “real-time” image capturing data rate. In this embodiment,the image data is provided to the processor/controller 104 in real time(i.e., while sensor unit 102 is measuring, sampling and/or capturingimage data). The input signals, in this embodiment, may include commandsfrom processor/controller 104, for example, start and configurationinformation.

In particular, in at least one example, the data rate may be in theorder of 200 Million pixels per second for a 3 cm×3 cm lithographicstepper printing field, a sensor array 106 having 100 Million sensorcells 200 each having a 3 μm pixel size, and an exposure rate of ½seconds per exposure. Further, where 8 bits are used to represent eachpixel's gray level, the data rate is in the range of 1.6 G bits/second.

It should be noted that, as mentioned above, the transmission data ratemay be reduced using a number of techniques including, for example, datacompression, noise reduction and buffering (elastic or otherwise).Assuming 2:1 data compression, a desired output bandwidth may be in therange of 800 M bits per second (Mbps). In short, there are manytechniques to reduce the bandwidth requirement; accordingly, all suchtechniques, whether now known or later developed, are intended to bewithin the scope of the present invention.

It should be further noted that in some embodiments, a Forward ErrorCorrection (FEC) technique may be employed to reduce the amount ofpotential re-transmission due to error or loss, if any, during wirelesstransmission.

In certain embodiment, the image data measured, sampled, and/or capturedby sensor unit 102 may not be transmitted to processor/controller 104 inreal time (i.e., while the image is being measured and the sensor unit102 is still on the stepper stage), but may be stored in memory 120(FIGS. 3B and 3C). After the data collection and after the sensor unit102 is unloaded from the stepper stage, the image data may be downloadedto processor/controller 104 through wired, wireless, and/or opticalcommunications, for example, using connector 122.

With reference to FIG. 3D, in another embodiment, sensor array 106 maybe disposed in, or integral with chuck 22 of lithographic equipment 10.In this embodiment, image sensor unit 102 need not be loaded into thelithographic equipment but may be positioned in the wafer plane (forexample, by chuck 22) during inspection, characterization and/orevaluation of photomask 26 and/or the optical components of lithographicequipment 10. As mentioned above, electrical power may be provided tothe components of image sensor unit 102 from lithographic equipment 10.Moreover, image sensor unit 102 may receive/provided data and commandsusing wired, wireless or optical communications.

The image sensor unit 102 of this embodiment may also include acontroller, a source of electrical power, data compression circuitry,communications circuitry, memory and/or connector, as described abovewith respect to FIGS. 3A, 3B and 3C. This circuitry (and the functionsperformed thereby) may be integrated into components and/or circuitry inlithographic equipment 10 or external thereto. For example, thefunctions and operations performed by the controller of image sensorunit 102, as described above, may be undertaken or performed by acontroller resident in lithographic equipment 10 or by a separate,dedicated device.

In addition, power to the components of image sensor unit 102 (forexample, sensor array 106) may be provided by lithographic equipment 10or by a dedicated power supply. Further, image sensor unit 102 mayinclude separate communications circuitry, for example, components toimplement wireless, wired and/or optical techniques; or image sensorunit 102 may employ the communication circuitry typically present inlithographic equipment 10.

In operation, image sensor unit 102 measures, collects, senses and/ordetects an aerial image produced or generated by the interaction betweenphotomask 26 and lithographic equipment 10 (whether in situ or not). Inone embodiment, the image data which is representative of the aerialimage is collected by repeatedly exposing sensor array 106 with aspatial shift (relative to the aerial image) between exposures. Aftereach exposure, the sensor array 106 provides a sparsely sampledsub-image frame, which may be referred to as a sub-image or sub-frame indiscussions below. The sub-images are interleaved to generate, create,provide and/or build-up the full-field image or to extract desiredinformation directly without reconstructing the aerial image.

In particular, with reference to FIGS. 12A-C and 13A-E, in oneembodiment, sensor array 106 is located in a first location relative tothe aerial image projected on the wafer plane (See, for example, FIG.13A). While in the first location, the aerial image is measured, sensed,detected and/or sampled by sensor cell 200 ax-200 gx (x=1 to 7) and thedata representative of the sample or measured values are provided to theother circuitry on image sensor unit 102 (for example, data compressioncircuitry 112, transmitter 114, and/or memory 120) for processing,transmission and/or storage.

The sensor array 106 is then moved to a second location, via chuck 22, adistance Δx from the first location (see, for example, FIG. 13B). In oneembodiment, Δx is substantially equal to the diameter or size ofapertures 206. In another embodiment, the spatial shift is substantiallyequal to the “effective” active area 202 of sensor cell 200. Where thediameter or size of apertures 206 is about 75 nm, the spatial shift of adistance Δx may be about 50 nm to about 75 nm.

While in the second location, the aerial image is again measured,sensed, detected and/or sampled by sensor cells 200 ax-200 gx (x=1 to7). The measured or sampled values (data representative of the aerialimage) are again provided to the other circuitry on image sensor unit102 (for example, data compression circuitry 112, transmitter 114,and/or memory 120) for processing, transmission and/or storage.

The sensor array 106 is then moved to a third location (a distance Δxfrom the second location) and the aerial image is again measured,sensed, detected and/or sampled by sensor cells 200 ax-200 gx (x=1 to 7)(see, for example, FIG. 13C). As before, the measured or sampled valuesare provided to the other circuitry on image sensor unit 102 forprocessing and/or storage.

In one embodiment, this data collecting or sampling process continues inthe x-direction until a portion of the aerial image that is collected bya given sensor cell 200 is contiguous (or substantially contiguous) withthe first location collected or sampled by an adjacent lateral sensorcell (See, FIG. 13D). Thereafter, sensor array 106 (via chuck 22) ismoved in the y-direction a distance Ay from the previous location (See,FIG. 13E). In one embodiment, Δy is substantially equal to the diameteror size of apertures 206. In another embodiment, the spatial shift Δy issubstantially equal to the “effective” active area 202 of sensor cell200. Where the diameter or size of apertures 206 is about 75 nm, thespatial shift of a distance Δy may be about 50 nm to about 75 nm.

While re-positioned a distance Δy, the aerial image is again measured,sensed, detected and/or sampled by sensor cells 200 a _(x)-200 g _(x)(x=1 to 7). The measured or sampled values are provided to the othercircuitry on image sensor unit 102 for processing, transmission and/orstorage. The sensor array 106 is then moved to a distance-Δx and theaerial image is again measured, sensed, detected and/or sampled bysensor cells 200 a _(x)-200 g _(x) (x=1 to 7). This process is continuedin the x and y directions until the aerial image (or portion thereof ismeasured, sensed, detected, collected and/or sampled. That is, thesensor array 106 may be moved, positioned and/or re-positioned in an xand y direction until the entire, or selected portion of the aerialimage has been measured, sensed, detected, collected and/or sampled.(See, for example, FIG. 12B) Thereafter (or simultaneously), the datameasured, collected, sensed, detected and/or sampled at each location isprocessed and compiled into a full image (or portion thereof that isrepresentative of the aerial image formed by the stepper onto the waferplane.

It should be noted that the data may also be collected in a vectorfashion, for example, using absolute x and y coordinates to effectivelyguide the exposure to a particular portion of the aerial image. The datais collected, measured, sensed, detected and/or sampled in the samemanner as described above. The aerial image may be processed andcompiled in the same manner as well. In this way, particular area(s) ofa mask may be examined in situ or certain locations or areas of theoptical system of lithographic equipment 10 may be examined.

The size of the spatial shift may be a “pixel” of the final capturedaerial image. In one embodiment, the spatial shift is equal to orsubstantially equal to the “effective” active area 202 of sensor cell200. In another embodiment, the spatial shift is equal to orsubstantially equal to the size of aperture 206. In either embodiment,the data is collected or sampled in a raster fashion, for example, using“small” relative movement in an x and/or y direction. In this way, eachexposure provides a sub-image or sub-frame; thereafter, all thesub-images are interleaved to build up the full-field (or partial-field)aerial image.

Since each sub-frame is captured by different exposures of the imagingfield by lithographic equipment 10, there may be slight misalignmenterrors or a given amount of alignment offset between the sub-frames.These errors or offset considerations may be caused by non-perfect stagepositioning repeatability. In a preferred embodiment, these errors oroffsets may be calibrated by aligning each sub-frame image to databaseimage, and, as such, be compensated in subsequent image processingsteps. This sub-frame-to-database alignment step is called sub-framealignment. Indeed, in one embodiment, historical data or the statisticsof the sub-frame offset represents the stage's positioningrepeatability, and hence may be used as information for steppermonitoring.

When the stage positioning is highly repeatability, for example,significantly smaller than of the pixel size (less than 20% of the pixelsize), it may be possible to perform inter-sub-frame alignment withoutthe database, to calibrate out the stage positioning offset errorsbetween exposures. This step maybe accomplished through the optimizationof the image and/or edge smoothness by fine adjustment of the relativeposition between the sub-frames. This alignment procedure, withoutdatabase image, is called inter-sub-frame alignment. Like sub-framealignment, the results of inter-sub-frame alignment may also be used asinformation for stepper monitoring.

In one embodiment, the image collecting and/or sampling techniqueemploys the highly precise spatial positioning and/or movement of chuck22 to collect and/or sample the aerial image. In another embodiment,chuck 22 and sensor 102 may remain stationary and the optics oflithographic equipment 10 and mask 26 may move.

As mentioned above, the sampled or measured values of sensor cells 200ax-200 gx (x=1 to 7) may be “pixels” of the aerial image. In oneembodiment, the “pixel” resolution may be equal (within 10% tolerance)or substantially equal (i.e., within 25% tolerance) to the dimensions ofapertures 206 ax-206 gx (x=1 to 7). The size and/or shape of apertures206 may be adjusted, designed or modified to accommodate a number ofconsiderations including, for example, the features of the aerial image(critical dimensions), the fabrication techniques of the sensor array106, the image acquisition time, the desired or necessary imageresolution, and/or the wavelength of light 16. While illustrated assubstantially circular in FIGS. 13A-E, the apertures 206 may besubstantially square, rectangular, triangular or oval. Indeed, any shapemay be implemented.

Moreover, the aperture may be shaped to match with certain test maskdesign pattern. For example, in certain application of the presentinvention such as focus analysis, the resolution along one direction maybe most significant/important. Under that circumstance, the dimension ofthe aperture in the other direction may be larger to achieve higherphoton passing rate.

It should be noted that the spatial shift Ax and/or Ay may be greaterthan or less than the diameter or size of apertures 206 and/or the“effective” active area 202 of sensor cell 200. In this regard, wherethe spatial shift Ax and/or Ay is less than the diameter or size ofapertures 206 and/or the “effective” active area 202 of sensor cell 200,system 100 may be over-sampling the aerial image to, for example,provide a highly precise aerial image. Indeed, the over-sampled data maybe used to confirm or verify the accuracy of surrounding data, oreliminate or minimize the need for data interpolation or extrapolation,or ensure that no spatial information is lost (i.e., the image betweensampled pixels can be exactly interpolated (this is called the Nyquisttheorem).

As described above, regardless of illumination, partial coherence, orreticle enhancement techniques on masks, in certain embodiments, themaximum spatial frequency in the light intensity distribution on waferplane is 2×NA/λ, where NA is the Numerical Aperture of the stepperprojection optics, and λ is the wavelength used in the imaging.Employing this relationship, the Nyquist sampling rate for aerial imagein a stepper is 4×NA/λ. As such, the pixel size may be at p=λ/(4×NA) orsmaller. For wavelength of 193 nm, and NA=0.75, the pixel size p may be64 nm or smaller. For wavelength of 248 nm, and NA=0.65, the pixel sizep may be 95 nm or smaller.

The pixel size may be equal or substantially equal to the shift betweensub-frames. Therefore, with reference to FIG. 12B, when the distancebetween sensor cells 200 (the cell size may be equal to or substantiallyequal to as the distance between neighboring apertures 206) is C, inorder to collect all spatial information, there will be a total of C/psub-frames along x-direction, and all of them repeated C/p times alongy-direction. As such, to collect or build-up a continuous full frameimage, (C/p)² sub-frames should be collected. This determines thethroughput of the full-field continuous aerial image capturing.

For example, where the size of sensor cell 200 is 9 μm, and a pixel sizeof 75 nm is employed, the total number of sub-frames required will be(9000/75)²=14400. Under this circumstance, where a stepper takes 0.5second to make one exposure, the total time required will be 7200seconds, which is 2 hours.

In certain embodiments, the sampled areas are not continuous. Forexample, when the aerial image is used to map out the linewidthvariation across the field (also called CD or critical dimension),collecting, sampling, measuring and/or sensing an entire full-fieldimage may not be necessary or useful. In this regard, it may besufficient to have blocks of small images distributed across the field,with each block sampled at Nyquist rate. With reference to FIG. 14A, inone embodiment, an array of image blocks where each block is sampled atNyquist, and the block array covers the entire field. This samplingstrategy may be called “block-mode sampling”. In this embodiment, acontinuous full field image is not generated, collected, sampled, sensed(compare FIG. 12B).

Using block-mode sampling, the image capturing time may be significantlyreduced. For example, using the same considerations as described above,assuming a 2.25 μm×2.25 μm area for each block is to be collected, thenumber of sub-frames is reduced to (2250/75)²=900, from the original14400. This is a 15× reduction in data collection time.

Further, block-mode sampling may facilitate using a sensor array 106having sensor cells 200 that are larger (for example, 10 μm, 20 μm, orlarger). In addition, this sampling technique may permit use of thepixel decimation mode that is available in most CCD chips operations.The pixel decimation mode bins multiple neighboring cells into a singlecell (for example, 1×2 or 2×2). This effectively enlarges the cell sizeand reduces the cell numbers, which thereby reduces the amount of datato be transmitted.

There are many applications that may employ block-mode sampling, forexample: (1) full-field CD metrology; (2) full-field stepper lensaberration calibration; (3) full-field stepper printing field distortioncalibration; and (4) full-field process window analysis. All suchapplications, whether now known or later developed, are intended to bewithin the scope of the present invention.

It should be noted that when implementing block-mode sampling, sporadicnon- functional cells in sensor array 106 may not affect thefunctionality of the system 100 because the sampling techniqueinherently produces a loss of certain blocks; however, the across fieldstatistics are still collected using the functional cells.

With reference to FIG. 14B, in another embodiment, the number ofsub-frames may be further reduced to two one-dimensional samples. Forexample, where the application of the system 100 is to calibrate thefocus plane location for x and y directional lines using a speciallydesigned grating mask, the one-dimensional sampling along both x and ymay suffice. The one-dimensional sampling may be either continuous ornot continuous. Under this circumstance, and using the sameconsiderations as described above, in a non-continuous application, thetotal number of sub-frames needed will be only (2250/75)+(2250/75)=60.In contrast, in the continuous application, the number of sub-frameswill be (9000/75)+(9000/75)=240.

With reference to FIG. 14C, in another embodiment, one-dimensionalsampling may be applied to any direction. In this regard, a 90-degreesampling technique is illustrated. Other one-dimensional samplingtechniques may also be implemented (for example, 0-degree and45-degree).

Sensor array 106 may be larger or smaller (or substantially larger orsmaller) than the aerial image to be measured. In those circumstanceswhere sensor array 106 is larger, certain sensor cells 200 may belocated outside or beyond the projected aerial image (in either an x, yor x-y direction) and as such, a portion of the data measured by certainsensor cells 200, a certain portion of the data measured by sensor cells200, or all of the data measured by certain cells 200 may be discardedbecause that data is not representative of, or related or pertinent tothe aerial image. While some data may be discarded or unnecessary, wheresensor array 106 is larger than the aerial image to be measured, anyconstraints, limitations or requirements of x-y alignment of the aerialimage on the wafer plane may be reduced or eliminated altogether.

In those circumstances where sensor array 106 is smaller than the aerialimage to be measured, chuck 22 may be positioned and repositioned, in atile or block like manner, to collect the entire image (see, forexample, FIGS. 15A-B, 19 and 20). The dimensions of each tile or blockmay be equal to or substantially equal to the dimensions of sensor array106. When positioned at a first location, sensor array 106 may collectan image data set, as described in detail above, of the aerial imageprojected at that position. Thereafter processor/controller 104 mayprocess the image data set measured, collected, sensed and/or detectedat each position to generate or create an aerial image for eachresponsive position. The processor/controller 104, in turn, may thenconnect or combine the pieces or portions of the aerial image in amosaic-like fashion, to produce a larger portion, or the entire, aerialimage.

In particular, with reference to FIGS. 15A and 15B, while sensor array106 is appropriately positioned, a first frame (i.e., Frame 1) issampled and collected, as described above with respect to FIGS. 12A-C,13A-E and/or 14A-C. Thereafter, sensor array 106 may be re-positioned tosample and collect a second frame (i.e., Frame 2), again as describedwith respect to FIGS. 12A-C, 13A-E and/or 14A-C. The other frames (ifany) may be collected in the same manner. The aerial image is generatedusing the data sampled and collected for each frame.

The present invention may be implemented to detect or inspect forcontamination, for example, mask contamination or optical lenscontamination. In this regard, the contamination refers to those thatcreate large-area but small-magnitude intensity change in the finalaerial image. In one embodiment, the aerial image may be collected,sampled and/or measured, below the Nyquist rate. With reference to FIG.16, the aperture size may be larger than the aperture size determinedabove. In this embodiment, the appropriate aperture size to be used maydepend on the size of the contamination defects that need to becaptured. It should be noted that both the aperture size (graphicallyrepresented by the dots) and pixel size (the spacing between dots) areenlarged.

In another embodiment, system 100 may collect image data using sensorunit 106 by scanning sensor array 106 across the image field. Withreference to FIG. 17, in one embodiment, a complete (or partial) aerialimage is collected, measured, sampled or built- up by scanning sensorcells 200 in one direction at a small angle to the array x-coordinatesuch that all y-adjacent pixels on the image are covered by one scan.

It should be noted that other scanning or imaging techniques using imagesensor unit 106 may be implemented to collect, measure, sample and/orbuild-up a complete (or partial) aerial image. All such techniques,whether now known or later developed, are intended to be within thescope of the present invention.

As mentioned above, the data which is representative of the aerial image(measured, collected, sampled, captured by sensor cells 200) isprocessed by processor/controller 104 to generate the aerial imageprojected on the wafer plane. In one embodiment, the aerial image isformed by the same imaging path of lithographic equipment 10 (includingmask 26) that is used to print product wafers. By monitoring the actualaerial image, the present invention enables the end-to-end, close-loopprocess optimization. That is, optimization from design and fabricationof mask 26, to lithographic equipment 10 selection, to set-up oflithographic equipment 10.

When employed as a lithography inspection system 100, the presentinvention may automatically compensate for the defects that areanticipated or expected to occur during processing, i.e., mask,illumination, optics, contamination, and interactions there between.Obtaining the aerial image projected on the wafer plane also enablesanalysis of the impact on printability and yield of a defect detectedand/or sensed, thereby allowing full lithography process integritycontrol.

The system of the present invention may also facilitate isolatingsources of errors or problems caused or produced during the lithographyprocess. For example, the impact of a given defect in mask 26 may bedetermined by substituting a mask having the same pattern thereon forthe “defective” mask. Since lithographic equipment 10 remains constant,if the defect is again detected or measured in the aerial image, thatdefect may be attributed to the optics of lithographic equipment 10.However, if the defect is not detected or measured, that defect may beattributed to the “defective” mask. In this way, the sources of errorsor problems may be isolated to the mask or lithographic equipment 10.

It should be noted that the image may also isolate imaging problems fromresist development and substrate etching, providing critical or usefulinformation for process development. Moreover, the present invention mayalso be used, in conjunction with software emulating the resistprocessing, to predict the developed resist image. Indeed, the presentinvention may be used, in conjunction with direct SEM inspection of thedeveloped resist image, to verify the above emulation. In fact, theaerial image captured using the present invention, in conjunction withSEM inspection of the final developed resist image, may be further usedto extract accurate resist models.

In addition to the capabilities of aerial image monitoring and defectinspection discussed above, the present invention(s) may also beimplemented in wafer pattern metrology. In this regard, the presentinvention(s) may facilitate full-field, non-destructive, in-situ, andreal circuit pattern or critical dimension measurements by comparing thesensed image to the mask pattern design database. In certain instances,it may be necessary to convert the polygon data within the designdatabase to intensity data. Alternatively, the data representative ofthe information sampled, measured, detected, and/or sensed may beconverted to data that permits comparison to the polygon data maintainedin the design database.

The inventions described herein may also be used in stepper calibration(for example, aberration and field distortion calibration). Informationcaptured, obtained and/or calculated during image processing, may alsobe used for stepper monitoring. For example, the sub-frame alignmentoffset may be used to monitor stage positioning repeatability, and theimage quality may be used to monitor stepper lens contamination and lensdrift.

It should be noted that one task of the algorithm(s) implemented byprocessor/controller 104 may be image processing to reconstruct theoriginal un-filtered aerial image. Such image processing may involvedeconvolution or other techniques of two-dimensional image processing.

As mentioned above, in certain embodiments, the image processingalgorithms may be implemented before a full image is received, sampled,measured and/or captured by sensor unit 102. For example,processor/controller 104 may begin processing data received from sensorunit 102 before a full image is provided and/or sampled, measured and/orcaptured by sensor unit 102. In this regard, processor/controller 104may initiate and implement decompression, data structure setup,sub-frame alignment, inter-sub-frame alignment, and noise reductionalgorithms.

As mentioned above, in certain applications, a database image isemployed to maintain the theoretical aerial image based on the maskpattern design and the ideal optics. As such, in certain embodiments,because the computation of the database image is extremely intensive, itmay be advantageous to compute the database image “offline” and storedin the image computer in certain data structure that is easy to beretrieved and assembled. This offline database computation may usestorage space, but the reduction in real time computation may presenteconomical architectural advantages for system 100. Furthermore, whenthe computed database is stored, it may be stored in compressed format(lossless compression) to minimize or reduce the necessary storagespace. Such compression may be very effective (for example, better than5:1) for database images, since there is no noise in the database image.

For some applications, for example, CD metrology, processing windowanalysis, and mask design verification, the aerial image may bereconstructed. Yet for some other applications, the actual aerial imageneed not be reconstructed, but the sensor image itself may suffice, forexample, image field placement distortion, and mask defect inspection.When performing Die-to-Die (D:D) mask inspection, direct comparisonbetween the sensor images from multiple dice may be suitable. ForDie-to-Database (D:DB) mask inspection, the database may be directlyrendered to its theoretical image under “ideal” stepper and sensorconfiguration, and, as such, allow the D:DB inspection by comparing thesensor image to that “theoretical” database image.

In those instances where mask 26 includes OPC or PSMdecoration/features, the database used in D:DB mask inspection may beeither the one with the decoration, or the one without decoration. Thedatabase with decoration is typically used to make the mask, and isexpected to be consistent with mask 26. The database without decorationis generally known as the “design-target” (i.e., the target on-waferimage which combines the effect from OPC/PSM decoration and the imagingpath of the stepper). When using database with decoration, the databaserendering should fully consider the stepper optics effect. When usingthe design-target database, the stepper imaging effect is alreadyembedded and hence need not be computed again.

In one embodiment, the D:DB inspection method may include thecomparisons of the: (1) decorated image to the sensor image orreconstructed aerial image (using sensor unit 102) and (2) design-targetto the sensor image or reconstructed aerial image. In this embodiment,the decoration is inspected or verified through using the sensor imageor reconstructed aerial image. For example, where there is an error inthe decoration (for example, the OPC software made a mistake indecoration), and the mask is made “correctly” that is, the decoration isaccurately produced according to the OPC software, the optical imageproduced by that mask will show that there is no defect when comparedwith the decorated database. However, the optical image produced by thatmask will reveal a defect when compared with the design-target, andhence an OPC decoration error may be detected.

Thus, the present invention may be employed, for example, in: (1)stepper development, including lens aberration calibration, focuscalibration, field distortion calibration, illumination calibration; (2)stepper qualification, including separation of stepper errors fromresist development and etching errors, aerial image quality assessment;(3) stepper monitoring, including contamination monitoring, stagepositioning repeatability monitoring, stepper aberration monitoring,illumination drift monitoring; (4) process development, includingprocess window analysis, resist model extraction; (5) full fieldmetrology, including linewidth (CD) measurement, contact energymeasurement; (6) mask inspection, including D:D and D:DB inspection,mask contamination inspection; (7) mask design verification, includingOPC and PSM decoration verification; (8) process optimization, includingmask-specific adjustment and centering of process window, selection ofoptimization of mask-stepper pairing, adjustment of stepper parameters(for example, illumination filter, partial coherence, pupil filter, andso on) using mask-specific aerial images; (9) design to processoptimization, including aerial image analysis to capture potentialyield-loss hot spots, Design-Rule-Checking (DRC) on aerial images; (10)design verification and optimization, for example, extraction ofelectrical performance information, such as resistance, current,voltage, timing, noise, power, etc from a set of aerial images, and thesubsequent use of such extract electrical performance data of thecircuit for design optimization; and (11) failure analysis, for example,use the aerial images to analyze the potential failure mechanism (e.g.,overlay-induce shorts) if the chip does not work as designed. Indeed,all applications of the present invention(s), whether now know or laterdeveloped, are intended to come within the scope of the presentinvention(s).

It should be noted that lithographic equipment 10 and/orprocessor/controller 104 may employ system 100, in conjunction withcontrol software of lithographic equipment 10, to enable rapid and/orreal-time optimization. In one embodiment, the system of the presentinvention may be combined with a specially designed mask to monitor thelithographic equipment 10, for example, optical aberration, fielddistortion, and illumination.

The system 100 may then provide the real-time feedback to controlsoftware of lithographic equipment 10 (for example the stepper) toimplement system modifications to minimize the aberrations and fielddistortion, and improve the illumination uniformity across the imagingfield.

In another embodiment, the system of the present invention may directlysense the aerial image of the production mask, and compute theadjustment to the stepper settings to optimize the aerial image quality.This may facilitate mask-stepper-combination-specific optimization. Forexample, where the mask has a slow spatial CD variation, the system ofthe present invention may measure and detect that CD variation andfeedback the suggested changes to the stepper illumination settingsacross the field to compensate the mask's CD non-uniformity. For certainareas that have a smaller CD than expected or permitted, the stepper mayadd more illumination dose to compensate for such an imperfection. Sucha feature may significantly enhance the parametric yield of thelithography process, since it is well known in the art that CDuniformity directly translates into the speed at which the IC chip canbe run.

In another example, the images captured-using the system of the presentinvention may be used to adjust and center, for each mask-steppercombination, the optimal process window, allowing more robust and higheryield IC fabrication.

The system of the present invention may also be implemented to optimizefor specific product masks. For example, where the locations of criticalpatterns are known, apertures 206 may be located to be more rapidly andeasily aligned with the critical patterns. Indeed, the shape ofapertures 206 may also be selected to better suit such an application.This may significantly improve the speed of image capturing, since thereis no need to capture the sub-frames that do not contain the criticalpatterns.

Further, the customized aperture shape may significantly improve theperformance of the monitoring. For example, the customized apertureshape may significantly improve monitoring gate linewidth CD in, forexample, a microprocessor. Thus, in those instances where the locationsof the critical-path transistors are known, apertures 206 may belocated, positioned or aligned with the location of the gates of thosetransistors in order to more rapidly and accurately monitor the CD ofsuch integrated circuits. Moreover, the shape of apertures 206 may alsomatch the gates.

Yet another application in analyzing the aerial image is to combineimages from multiple exposures. In this regard, for some PSM designs,multiple masks are made to expose the same layer. For example, in oneimplementation of alternating-PSM (see, for example, U.S. Pat. No.6,228,539), a first mask has multiple phases, and a second mask (calledtrim mask) has only a single phase, and both masks are exposed on thesame layer to create the desired effect in the photo-resist. The systemof the present invention may record the sensed aerial image from thefirst mask, then the sensed aerial image from the second mask is addedto the first aerial image, and hence obtain the combined effect of thetwo masks in the photo-resist. The combined image may then be used tocompare with the design-target image, for mask inspection, or forverifying the PSM design and decorations.

In the case of multiple masks, the individually captured aerial imagesof each mask may be further used to optimize the combination in actualprocess, for example, relative dose. The individually captured aerialimages may also be used to analyze the process tolerance, for example,the overlay tolerance between the two masks, and where the mostdefect-prone spots are located. This inter-layer analysis may not onlybe applied to the multiple-mask-single-layer case as described above,but also between different adjacent layers on the circuit, for example,to analyze and optimize the interlayer overlay tolerance between thepoly-gate layer and the contact layer using the aerial images from thosetwo layers.

Yet another potential application of aerial images captured frommultiple exposures is to analyze and inspect the phase information inPSM. For example, multiple aerial images can be captured at differentfocus planes for a PSM, and the images from these multiple focus planescan be used to extract the phase shift amount for each phase-shiftregion on the PSM, and be compared and verified again design.

The system of the present invention may also be used in StatisticalProcess Control (“SPC”). In this regard, the system 100 monitors thestepper performance every time it is used, and hence tracks the historyof the performance of the stepper to provide, for example, preventivemaintenance alerts.

The system of the present invention may also be used to inspect andoptimize certain maskless lithography technologies. “Masklesslithography technology” generally refers to the lithography techniquesthat do not use a mask, rather the patterns are written on the waferdirectly by the lithography tool, e.g., an electron-beam direct-writelithography tool. One category of maskless lithography technologiesincludes a “programmable mask”, i.e., the pattern is still defined by a“mask”, but the mask is programmable using the database and directlyresides in a lithography tool, e.g. a micro-mirror array where eachmirror can turn on and off of a pixel.

In the maskless technology that uses a programmable mask, there will beno mask to inspect. One way to assure the quality of the programmed maskand the quality of the printed pattern is to directly measure, analyze,and/or inspect the aerial image generated or produced by this masklesslithography system using the sensor unit 102 and the techniquesdescribed above. Under this circumstance, the aerial image analysis maybe directly feedback to the maskless lithography system, to adjust andoptimize the programming of the programmable mask, and thereby enabledirect lithography quality optimization.

As mentioned above, in one aspect the present invention may be (or beimplemented in) an imaging system that generates or produces the same orsubstantially the same aerial image (or producing, sampling, collectingand/or detecting information relating to), with the same orsubstantially the same spatial resolution, as certain lithographicequipment (for example a particular stepper system having a given set ofparameters, features or attributes). In this regard, the imaging systememulates that lithographic equipment. Thus, in this embodiment, theimaging system includes a precision mechanical movement stage having thesame or substantially the same mechanical precision and controllabilityas lithographic equipment. The imaging system may be employed as astandalone aerial image monitoring tool that may be used in thereviewing of the aerial image of a mask under the predetermined opticsub-system.

The stepper-like tool (stepper, mini-stepper, or other imaging optics)together with system (or portions thereof described above with respectto image sensor unit 102 and processor/controller 104 may be astand-alone aerial image inspection tool. This stand-alone tool may beemployed, for example, to perform mask inspection and/or mask defectreview. In this embodiment, the aerial image is sensed directly, athigh-NA and at the same magnification as on the product wafer. As such,not only is the wavelength and partial coherence matched (orsubstantially matched), but also the NA is matched (or substantially)with actual steppers, eliminating the potential deviation from actualaerial image when vector field in EM wave is considered. In this regard,the fidelity of the aerial image may be improved.

It should be noted that the discussions of, for example, image sensorunit 102 and processor/controller 104, are fully applicable to thisaspect of the present invention. For the sake of brevity, thosediscussions will not be repeated.

There are many inventions described and illustrated herein. Whilecertain embodiments, features, attributes and advantages of theinventions have been described and illustrated, it should be understoodthat many other, as well as different and/or similar embodiments,features, materials, attributes, structures and advantages of thepresent inventions, are apparent from the description, illustration andclaims. As such, the embodiments, features, materials, attributes,structures and advantages of the inventions described and illustratedherein are not exhaustive and it should be understood that such other,similar, as well as different, embodiments, features, materials,attributes, structures and advantages of the present inventions arewithin the scope of the present invention.

It should be noted that while the present invention(s) is described inthe context of measuring, inspecting, characterizing and/or evaluatingoptical lithographic equipment, methods, and/or materials usedtherewith, for example, photomasks, the present invention may be used tomeasure, inspect, characterize and/or evaluate other optical systems.Indeed, the image sensor unit described herein may be used to measure,inspect, characterize and/or evaluate microscopes and telescopes. Or,the present invention can be combined with a microscope or telescopeoptics and a precise mechanic stage, to realize sub-optical-wavelengthresolution in image sensing. As such, any optical system, method and/ormaterial used therewith, whether now known or later developed, areintended to be within the scope of the present invention.

Moreover, it should be noted that while the present invention(s) isdescribed generally in the context of integrated circuit fabrication,the present invention(s) may be implemented in processes to manufactureother devices, components and/or systems including, for example,photomasks, hard disk drives, magnetic thin-film heads for hard diskdrives, flat panel displays, and printed circuit board. Indeed, thepresent invention(s) may be employed in the fabrication of any devices,components and/or systems, whether now known or later developed, thatmay benefit (in whole or in part) from the present invention(s).

For example, in other applications or industries, substrate 118 may takea different form factor and may be made from different materials. Forexample, in photomask manufacturing, using laser exposure or otheroptical imaging exposure techniques, the substrate may be a mask blank(glass or quartz), or other material with the same shape of a photomask(which maybe a square plate of 5 or 6 inches each side, with thicknessof a few millimeters). In Flat Panel Display manufacturing, thesubstrate may be a high quality glass plate of a predetermined shape andsize. In hard disk drive manufacturing, the substrate is alsowafer-like, but made from different materials. In printed circuit board(PCB) manufacturing, the substrate is a circuit board. It should benoted that the present invention(s) may be implemented using the given(different) substrate form-factors and/or materials of the particularapplication in which the invention is implemented. Such substrates mayinclude one, some or all of the functionalities and capabilitiesdescribed herein. Indeed, other functionalities and capabilities may bedesired depending upon the particular application in which the inventionis implemented.

It should be further noted that there are many techniques and materials(and, as a result, structures created thereby) for enhancing the spatialresolution and/or sensitivity of sensor cells 200. Indeed, there aremany techniques and permutations of depositing, growing and/or formingopaque film 204, apertures 206, detection enhancement material 208and/or photon-conversion material 210. All techniques and materials, andpermutations thereof, that enhance, limit or restrict the spatialresolution of active areas 202 of sensor cells 200, whether now known orlater developed, are intended to be within the scope of the presentinvention.

Further, while apertures 206 have been generally illustrated as havingsubstantially vertical sidewalls, the sidewalls may include a taperededge. Such sidewalls may be formed using a variety of fabricationtechniques. For example, apertures 206 may be formed using a combinationof anisotropic and isotropic etching techniques that form a tapering atthe edges of the sidewalls after the relatively vertical etch iscompleted.

Indeed, another technique of limiting, restricting or enhancing thespatial resolution or sensitivity of sensor cells 200 of sensor array106 is to employ anomalously high transmission of light or photons inarrayed apertures in a film (see, for example “Extraordinary OpticalTransmission through Sub-wavelength Hole Arrays”, T. W. Ebbesen et al.Nature 391, 667, (1998) and T. J. Kim et al. “Control of OpticalTransmission through Metals Perforated with Sub-wavelength Hole Arrays”,Optics Let. 24 256 (1999), the contents of which are hereby incorporatedby reference). Where the film includes more than one aperture per activearea/sensor cell, the system 100 may employ deconvolution or other imageprocessing techniques to appropriately characterize, sense, detect,measure and/or sample the aerial image of mask 26 as projected at thewafer plane. Indeed, more than one aperture may be avoided by usingblind (partially milled or etched) apertures or other surfacemodifications.

In addition, there are many techniques implemented by the structures ofthe inventive sensor unit. For example, communications between sensorunit 102 and processor/controller 104 may be via electronic, optical,wired or wireless. As such, suitable circuitry (for example,transmitters, receivers, connectors, data compression circuitry,controller and memory) may be implemented on or in sensor unit 102 toaccommodate the various means of communication (see, for example, FIG.3A (primarily wireless), FIG. 3B (wireless, optical and/or wired) and/orFIG. 3C (primarily optical and/or wired)). Indeed, all forms ofcommunication, whether now known or later developed are intended to fallwithin the scope of the present invention.

Moreover, the communications of the data representative of the aerialimage may be during data collection and/or after data collection. Suchcommunication may be while sensor unit 102 resides in the lithographicequipment (for example, during data collection) or while the sensor unitis external to the lithographic equipment (for example, after datacollection). Indeed, sensor unit 102 may include sufficient memory (forexample, DRAM, SRAM, or flash) to store some or all of the datarepresentative of the aerial image in order to increase the flexibilityof data transmission (i.e., when such data is transmitted and how suchdata is transmitted). Indeed, in those instances where sensor unit 102is transmitting data during collection, memory 120 may be employed as abuffer for such data communications/transmission.

In addition, it should be noted that although sensor cells 200 of sensorarray 106 have been described above to be arranged in an arrayconfiguration, other configurations may be suitable. Moreover, thenumber of sensor cells 200 employed to comprise sensor array 106 may beselected based on various considerations, including, for example, datacollection time, the size of the aerial image at the wafer plane, thespatial resolution of the data collection, and/or the spatial resolutionof active areas 202 of sensor cells 200.

It should be further noted that the dimensions of sensor array 106 maydepend on a number of considerations including, for example, the numberof sensor cells 200 employed, the size of the aerial image at the waferplane, the spatial resolution of the data collection, the spatialresolution of active areas 202 of sensor cells 200, constraints based onthe data collection time, and/or data collection techniques. In oneembodiment, the sensor array 106 is approximately 27 mm×33 mm and theaerial image (at the wafer plane) is about 26 mm×32 mm.

As mentioned above, sensor cells 200 may be CCDs, CMOS sensor devices,photodiode devices or the like. Moreover, sensor cells 200 may be acombination of such devices. Indeed, any device(s) that measures,senses, detects and/or samples light, whether known or later developed,is intended to fall within the scope of the present invention.

Moreover, sensor array 106 may be comprised of a plurality of sub-sensorarrays. For example, with reference to FIGS. 18A and 18B, sensor array106 is comprised of sub-sensor arrays 106 a-d. Each sub-sensor array 106a-d may be comprised of sensor cells 200 as illustrated in FIGS. 4-10and/or described above. Such a configuration may provide an advantage ofimage data collection, and the speed thereof, since arrays 106 a-d aresmaller than the combined sensor array 106 and associated interfacecircuitry may collect and compile the information more rapidly, therebyreducing the inspection time. Further, it also reduces the requirementon the size of a single sensor array unit.

FIG. 19 illustrates one embodiment where multiple sub-sensor arrays arecombined to construct a larger image sensor array. The sub-sensor arrays106 a-f in FIG. 19 are arranged in such a way that sensor array 106(which includes 106 a-f) is moved, relative to the field, four times tocover the area between the chips. In one embodiment, the operationsequence may be: (1) use the sub-frame capturing, then buildup the imagefor the first location of each sensor chip; (2) step the array to aprevious uncovered area in the imaging field (represented by a differentpattern or shading in FIG. 19; (3) repeat the sub-frame capturingprocess again to build-up the image in this new chip array location; (4)move the array, repeat the process until all area in the imaging fieldis covered.

It should be noted that it is acceptable to have double coverage (i.e.,overlap between frames) in the butting areas between the four locationsof the sensor array. So, the areas covered by different chip arraylocation do not need to tile up seamlessly.

Another scanning or tile-up technique, though it uses slightly moresensor chips (106 a-h), is illustrated in FIG. 20. In this embodiment,the array is positioned in three different locations relative to theimaging field, and hence this embodiment increases the image-capturingthroughput.

It should also be noted that, for applications that use block-modesampling, it may be acceptable to miss or eliminate the image blocksbetween the chips that are covered by the sensor readout circuitry andbonding pads. In that case, the tiling can be as simple as tiling up thesensor chips one to another, like the scheme illustrated in FIG. 18A-B.This configuration/technique allows the use of a single location of thechip array relative to the image, and hence avoid the throughput hitdescribed in association with FIGS. 19 and 20.

Finally, it should be further noted that the term “circuit” may mean,among other things, a single component or a multiplicity of components(whether in integrated circuit form or otherwise), which are activeand/or passive, and which are coupled together to provide or perform adesired function. The term “circuitry” may mean, among other things, acircuit (whether integrated or otherwise), a group of such circuits, aprocessor(s), a processor(s) implementing software, or a combination ofa circuit (whether integrated or otherwise), a group of such circuits, aprocessor(s) and/or a processor(s) implementing software. The term“data” may mean, among other things, a current or voltage signal(s)whether in an analog or a digital form. The term “sample” means, amongother things, measure, sense, inspect, detect, capture and/or evaluate.Similarly, the phrase “to sample” or similar, means, for example, tomeasure, to sense, to inspect, to detect, to capture, to evaluate, torecord, and/or to monitor.

1-40. (canceled)
 41. An image sensor unit, for use with photolithographic equipment, the image sensor unit comprising: a substrate having a wafer or wafer-like shaped profile; a sensor array, integrated into the wafer-shaped substrate, the sensor array including: a plurality of sensor cells wherein each sensor cell includes an active area to sense light of a predetermined wavelength that is incident thereon; and a film, disposed over the active areas of the plurality of sensor cells and comprised of a material that impedes passage of light of the predetermined wavelength, wherein the film includes a plurality of apertures which are arranged such that an aperture of the plurality of apertures overlies an active area of a corresponding sensor cell to expose a portion of the active area and wherein light of the predetermined wavelength is capable of being sensed by the portion of the active area that is exposed by the corresponding aperture.
 42. The image sensor unit of claim 41 further including a transparent medium, having a predetermined refractive index, disposed on the sensor array.
 43. The image sensor unit of claim 41 further including electrical contacts, disposed on or in the substrate, to provide a communication path with an external device.
 44. The image sensor unit of claim 41 further including electrical contacts, disposed on or in the substrate, to receive electrical power from an external device.
 45. The image sensor unit of claim 41 further including electrical contacts, disposed on or in the substrate, to output data to an external device.
 46. The image sensor unit of claim 41 further including electrical contacts, disposed on or in the substrate, to input control signals from an external device.
 47. The image sensor unit of claim 41 wherein the film is disposed between the active areas of the sensor cells and a protective outer layer of the sensor array.
 48. The image sensor unit of claim 41 wherein the film is disposed on a protective outer layer of the sensor array.
 49. The image sensor unit of claim 41 further including wireless communications circuitry, disposed on or in the substrate, to provide data to an external device.
 50. The image sensor unit of claim 49 wherein the wireless communications circuitry provides data during collection of image data by the sensor array.
 51. The image sensor unit of claim 41 wherein the sensor cells are charge coupled devices, CMOS devices or photodiodes.
 52. The image sensor unit of claim 41 further including photon-conversion material, disposed: (i) over the sensor array and between the film and the plurality of sensors, (ii) within the plurality of apertures of the film or (iii) on the sensor array.
 53. The image sensor unit of claim 41 wherein the image sensor unit further includes data storage circuitry, coupled to the sensor array and integrated into the substrate, to store the data from the sensor array.
 54. The image sensor unit of claim 41 further including a controller, integrated into or disposed on the substrate, to instruct the sensor array when to sample the intensity of light.
 55. A system to collect image data which is representative of an aerial image of a mask that is projected, by an optical system, on a wafer plane of lithographic equipment, the system comprising: an image sensor unit, disposed on the moveable platform, to collect data which is representative of the aerial image of the mask, the image sensor unit includes: a substrate adapted to be disposed on a platform of the lithographic equipment; a sensor array, disposed on or in, or integrated into the substrate, wherein the sensor array is capable of being located in the wafer plane, the sensor array includes: a plurality of sensor cells wherein each sensor cell includes an active area to sense light of a predetermined wavelength that is incident thereon; and a film, disposed over the active areas of the plurality of sensor cells and including a material that impedes passage of light of the predetermined wavelength, wherein the film includes a plurality of apertures which are arranged such that an aperture of the plurality of apertures overlies an associated active area of a corresponding sensor cell to expose a portion of the associated active area and wherein light of the predetermined wavelength is capable of being sensed by the portion of the active area that is exposed by the associated aperture.
 56. The system of claim 55 further including a controller, disposed in the lithographic equipment and coupled to the image sensor unit, to control the operation of the image sensor unit.
 57. The system of claim 55 further including a controller, coupled to the image sensor unit and disposed externally to the lithographic equipment, to control the operation of the image sensor unit.
 58. The system of claim 55 wherein the image sensor unit further includes a controller, coupled to the sensor array and integrated into or disposed on the substrate, to control the operation of the image sensor unit.
 59. The system of claim 55 wherein the image sensor unit further includes electrical contacts, disposed on or in the substrate, to provide a communication path with the lithographic equipment.
 60. The system of claim 55 wherein the image sensor unit further includes electrical contacts, disposed on or in the substrate, to receive electrical power from lithographic equipment.
 61. The system of claim 55 wherein the film of the image sensor unit is disposed between the active areas of the sensor cells and a protective outer layer of the sensor array.
 62. The system of claim 55 wherein the film of the image sensor unit is disposed on a protective outer layer of the sensor array.
 63. The system of claim 55 wherein the image sensor unit further includes wireless communications circuitry, disposed on or in the substrate, to provide data to the lithographic device during or after collection of image data by the sensor array.
 64. The system of claim 55 wherein the image sensor unit further includes wireless communications circuitry, disposed on or in the substrate, to provide data to the processor/controller during or after collection of image data by the sensor array.
 65. The system of claim 55 wherein the sensor cells of the image sensor unit are charge coupled devices, CMOS devices or photodiodes.
 66. The system of claim 55 wherein the image sensor unit further includes data storage circuitry, coupled to the sensor array and disposed on or integrated into the substrate of the sensor array unit, to store the data from the sensor array.
 67. The system of claim 55 wherein the image sensor unit further includes a controller, integrated into or disposed on the substrate, to control the operation of the sensor array.
 68. An image sensor unit, for use with photolithographic equipment, the image sensor unit comprising: a substrate adapted to be disposed on a platform of the lithographic equipment; a sensor array, disposed on or in, or integrated into the substrate, the sensor array including: a plurality of sensor cells wherein each sensor cell includes an active area to sense light of a predetermined wavelength that is incident thereon; and a film, disposed over the active areas of the plurality of sensor cells and comprised of a material that impedes passage of light of the predetermined wavelength, wherein the film includes a plurality of apertures which are arranged such that an aperture of the plurality of apertures overlies an active area of a corresponding sensor cell to expose a portion of the active area and wherein light of the predetermined wavelength is capable of being sensed by the portion of the active area that is exposed by the corresponding aperture.
 69. The image sensor unit of claim 68 further including electrical contacts, disposed on or in the substrate, to receive electrical power from an external device.
 70. The image sensor unit of claim 68 further including electrical contacts, disposed on or in the substrate, to provide a communication path with an external device.
 71. The image sensor unit of claim 68 wherein the film is disposed between the active areas of the sensor cells and a protective outer layer of the sensor array.
 72. The image sensor unit of claim 68 wherein the film is disposed on a protective outer layer of the sensor array.
 73. The image sensor unit of claim 68 wherein the sensor cells are charge coupled devices, CMOS devices or photodiodes.
 74. The image sensor unit of claim 68 wherein the image sensor unit further includes: a controller, integrated into or disposed on the substrate, to instruct the sensor array when to sample the intensity of light; and data storage circuitry, coupled to the sensor array and integrated into or disposed on the substrate, to store the data which is representative of the intensity of light sampled by the sensor array. 